What is meant by “buy-side firm” and “sell-side firm”?
Traditionally, dealers and broker-dealers were in contact with the actual producers of a product or issuers of a security, selling it at the exchange on their behalf.  Consumers would traditionally be on the buy side, of course. These days, anyone can enter the market on either side.  Even if you don't hold the security or product, you could sell it, and take on the risk of having to stock up on it by the delivery date in exchange for cash or other securities.  On the other side, if you can't hold the product or security you could still buy it, taking on the risk of having to dispose of it somehow by delivery in exchange for cash or other securities. In either case you (the sell-side) take on risk and provide products/securities/cash.  This is most commonly known as market making.  Modern literature coins the terms liquidity taker (buy-side) and liquidity provider (sell-side).  Even more accurately, risk management literature would use the terms risk-taker (sell-side) and risk spreader or risk reducer (buy side). This is quite illustrative in modern abstract markets.  Take a market that allows for no offsetting or hedging because the product in question is abstract or theoretical, e.g. weather trading, volatility trading, inflation trading, etc.  There's always one party trying to eliminate dependence on or correlation to the product (the risk reducer, buy-side) and the counterparty taking on their risk (sell-side).
I would suggest equity research, or as mentioned, consulting. You could go into IB. Your main hindrance is your age, how long has it been since you finished your PhD?  Equity Research: you will analyze companies, on an individual and micro basis, and provide macro point of views on the industry etc.   Sales/Trading: you will not get a job in trading, sales...maybe, if you get a bank large enough that has a healthcare/industrial chemicals sales positions, but this is a job that requires you to be able to sell your bank's point of view to large, very sophisticated clients, and provide them with better ideas than other sales guys, so that they will trade with your bank...can you learn finance and the industry fast enough? You would be better off working in a buy side shop (there are tons in boston)  IB: never met anyone that likes ib. depends on the bank but even mid market small banks it is 80hr weeks on avg. bulge bracket its 100. but you would likely start as an associate, (if at all) so that would go down really fast, (3-5 yrs to vp)  If you went to a top tier school, find alum from your school that work at banks and talk to them first, a 30 min conversation with anyone is incredibly useful. Just ask them how to get in. Also make sure you know all the capital markets firms in your area, know what all the fields are from a basic level (read the shit on wallstreetoasis etc) so that you dont waste time when talking to people.   You will likely need a CFA level 1 to get any traction, unless you can find some people that are willing to pull for you, which you will find is actually more simple than it seems - people love helping their alma matter, and every firm is always looking for smart people. anyways, sign up for the december 2012 cfa exam, and download/buy the schweser notes (don't read the actual books) this will be a great refresher about finance and economics even if you don't end up switching careers.  actual answers to your questions 1) yes 2) start as an associate in ib, spend 3 years doing bs, and workin average 90hrs a week, either quit of become vp and start selling work vs doing it 3) ib: immediate sales/trading: immediate, buy side: varies on the firm, size, performance, could be immediate, could be the year after, or you could get fired after 3 months because your phd isnt as useful as they thought it was. 4) mentioned above...a few years, its managable, suck it up 5) no sorry   goodluck This is correct. The most rapidly expanding areas in finance resemble computer science more than they resemble traditional finance. The compliance and legal side of things, however, is only getting more and more complicated. At my firm, the compliance personnel outnumber the traders three to one. "Simplest way to answer this is that on margin, one is using borrowed assets and thus there are strings that come with doing that. Thus, if the amount of equity left gets too low, the broker has a legal obligation to close the position which can be selling purchased shares or buying back borrowed shares depending on if this is a long or short position respectively. Investopedia has an example that they walk through as the call is where you are asked to either put in more money to the account or the position may be closed because the broker wants their money back. What is Maintenance Margin? A maintenance margin is the required   amount of securities an investor must hold in his account if he either   purchases shares on margin, or if he sells shares short. If an   investor's margin balance falls below the set maintenance margin, the   investor would then need to contribute additional funds to the account   or liquidate stocks in the account to bring the account back to the   initial margin requirement. This request is known as a margin call. As discussed previously, the Federal Reserve Board sets the initial   margin requirement (currently at 50%). The Federal Reserve Board also   sets the maintenance margin. The maintenance margin, the amount of   equity an investor needs to hold in his account if he buys stock on   margin or sells shares short, is 25%. Keep in mind, however, that this   25% level is the minimum level set, brokerage firms can increase, but   not decrease this level as they desire. Example: Determining when a margin call would occur. Assume that an   investor had purchased 500 shares of Newco's stock. The shares were   trading at $50 when the transaction was executed. The initial margin   requirement on the account was 70% and the maintenance margin is 30%.   Assume no transaction costs. Determine the price at which the investor   will receive a margin call. Answer: Calculate the price as follows: $50 (1- 0.70) = $21.43 1 - 0.30 A margin call would be received when the price of Newco's stock fell   below $21.43 per share. At that time, the investor would either need   to deposit additional funds or liquidate shares to satisfy the initial   margin requirement. Most people don't want ""Margin Calls"" but stocks may move in unexpected ways and this is where there are mechanisms to limit losses, especially for the brokerage firm that wants to make as much money as possible. Cancel what trade? No, the broker will close the position if the requirement isn't kept. Basically think of this as a way for the broker to get their money back if necessary while following federal rules. This would be selling in a long position or buying in a short sale situation. The Margin Investor walks through an example where an e-mail would be sent and if the requirement isn't met then the position gets exited as per the law." "Exposure is the amount of money that you are at risk of losing on a given position (i.e. on a UST 10 year bond), portfolio of positions, strategy (selling covered calls for example), or counterparty, usually represented as a percentage of your total assets. Interbank exposure is the exposure of banks to other banks either through owning debt or stock, or by having open positions with the other banks as counterparties. Leveraging occurs when the value of your position is more than the value of what you are trading in. One example of this is borrowing money (i.e. creating debt for yourself) to buy bonds. The amount of your own funds that you are using to pay for the position is ""leveraged"" by the debt so that you are risking more than 100% of your capital if, for example, the bond became worthless). Another example would be buying futures ""on margin"" where you only put up the margin value of the trade and not the full cost. The problem with these leveraged positions is what happens if a credit event (default etc.) happens. Since a large amount of the leverage is being ""passed on"" as banks are issuing debt to buy other banks' debt who are issuing debt to buy debt there is a risk that a single failure could cause an unravelling of these leveraged positions and, since the prices of the bonds will be falling resulting in these leveraged positions losing money, it will cause a cascade of losses and defaults. If a leveraged position becomes worth less than the amount of real (rather than borrowed or margined) money that was put up to take the position then it is almost inevitable that the firm in that position will default on the requirements for the leverage. When that firm defaults it sparks all of the firms who own that debt to go through the same problems that it did, hence the contagion." This would clear out a lot more. 1) Leverage is the act of taking on debt in lieu of the equity you hold. Not always related to firms, it applies to personal situations too. When you take a loan, you get a certain %age of the loan, the bank establishes your equity by looking at your past financial records and then decides the amount it is going to lend, deciding on the safest leverage. In the current action leverage is the whole act of borrowing yen and profiting from it. The leverage factor mentions the amount of leverage happening. 10000 yen being borrowed with an equity of 1000 yen. 2) Commercial banks: 10 to 1 -> They don't deal in complicated investments, derivatives except for hedging, and are under stricter controls of the government. They have to have certain amount of liquidity and can loan out the rest for business. Investment banks: 30 to 1 -> Their main idea is making money and trade heavily. Their deposits are limited by the amount clients have deposited. And as their main motive is to get maximum returns from the available amount, they trade heavily. Derivatives, one of the instruments, are structured on underlyings and sometimes in multiple layers which build up quite a bit of leverage. And all of the trades happen on margins. You don't invest $10k to buy $10k of a traded stock. You put in, maybe $500 to take up the position and borrow the rest of the amount per se. It improves liquidity in the markets and increases efficiency. Else you could do only with what you have. So these margins add up to the leverage the bank is taking on. Buy and hold doesn't have an exact definition, as far as I know.  In my opinion, it's offered as a contrast to those who trade too frequently, or panic every time the market drops 2%.  For the general market, e.g. your S&P index holdings. You sell to rebalance to your desired asset allocation. As a personal example, at 50, I was full up invested, 95%+ in stocks. When my wife and I were retired (i.e. let go from company, but with no need to go back to work) I started shifting to get to a more sane allocation, 80/20. The ideal mix may be closer to 60/40.  Also, there are times the market as a whole is overvalued as measure by P/E and/or CAPE, made popular by Nobel Prize winning Robert Shiller. During these times, an allocation shift might make sense.  For the individual stocks, you had best have a strategy when you buy. Why did you buy XYZ? Because they had promise, decent company with a good outlook for their product? Now that they are up 300%, can they keep gaining share or expand their market? Sometimes you can keep raising the bar, and keep a company long term, really long. Other times, the reason you bought no longer applies, they are at or above the valuation you hoped to achieve.  Note - I noticed from another question, the OP is in the UK. I answer this my from US centric view, but it should still apply to OP in general. The question was not tagged UK when I replied. "You are likely making an assumption that the ""Short call"" part of the article you refer to isn't making: that you own the underlying stock in the first place. Rather, selling short a call has two primary cases with considerably different risk profiles. When you short-sell (or ""write"") a call option on a stock, your position can either be: covered, which means you already own the underlying stock and will simply need to deliver it if you are assigned, or else uncovered (or naked), which means you do not own the underlying stock. Writing a covered call can be a relatively conservative trade, while writing a naked call (if your broker were to permit such) can be extremely risky. Consider: With an uncovered position, should you be assigned you will be required to buy the underlying at the prevailing price. This is a very real cost — certainly not an opportunity cost. Look a little further in the article you linked, to the Option strategies section, and you will see the covered call mentioned there. That's the kind of trade you describe in your example." At any given time there are buy orders and there are sell orders.  Typically there is a little bit of space between the lowest sell order and the highest buy order, this is known as the bid/ask spread.  As an example say person A will sell for $10.10 but person B will only buy at $10.00.  If you have a billion shares outstanding just the space between the bid and ask prices represents $100,000,000 of market cap. Now imagine that the CEO is in the news related to some embezzlement investigation.  A number of buyers cancel their orders.  Now the highest buy order is $7.  There isn't money involved, that's just the highest offer to buy at the time; but that's a drop from $10 to $7.  That's a change in market cap of $3,000,000,000.  Some seller thinks the stock will continue to fall, and some buyer thinks the stock has reached a fair enterprise value at $7 billion ($7 per share).  Whether or not the seller lost money depends on where the seller bought the stock.  Maybe they bought when it was an IPO for $1.  Even at $7 they made $6 per share. Value is changing, not money.  Though it would be fun, there's no money bonfire at the NYSE.