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What does it mean “sell on ask” , “sell on bid” in stocks?
Bid and ask prices are the reigning highest buy price and lowest sell price in the market which doesn't mean one must only buy/sell at thise prices. That said one can buy/sell at whatever price they so wish although doing it at any other price than the bid/ask is usually harder as other market participants will gravitate to the reigning bid/ask price. So in theory you can buy at ask and sell at bid, whether or not your order will be filled is another matter altogether.