What is the definition of Eurodollar? What are Eurodollars? How are they distinct from plain old dollars? Asking as an interested but non-specialist outsider, though I do know what demand deposits are and am familiar with the conversation regarding fractional reserve banking.
The definition of Eurodollar is (see Investopedia):

The term eurodollar refers to U.S. dollar-denominated deposits at foreign banks or at the overseas branches of American banks.

They are distinct from regular dollars because they are not held within the US, and as a consequence eurodollars are generally not subject to regulations by the Fed (e.g. reserve requirements) and other US banking regulations (like the federal deposit insurance). Since historically in the past most of the dollar denominated deposits were held in Europe (this was to considerable  extent due to the Marshall plan which led to relatively high circulation of dollars in the Europe) they became known as &quot;eurodollars.&quot;
If you want to learn more about history of eurodollars and the mechanisms behind them then you can have look at Schenk(1998): The origins of the Eurodollar market in London, or Einzig &amp; Quinn (1964): The Euro-dollar system: practice and theory of international interest rates.