Eurodollar basically US dollar denominated deposits at foreign banks outside US.

Originally, dollar-denominated deposits not subject to U.S. banking regulations were held almost exclusively in Europe; hence the name eurodollars. These deposits are still mostly held in Europe, but they're also held in such countries as the Bahamas, Canada, the Cayman Islands, Hong Kong, Japan, the Netherlands Antilles, Panama and Singapore. Regardless of where they are held, such deposits are referred to as eurodollars.

Since the eurodollar market is relatively free of regulation, banks in the eurodollar market can operate on narrower margins than banks in the United States. Thus, the eurodollar market has expanded largely as a means of avoiding the regulatory costs involved in dollar-denominated financial intermediation.