A Cash Advance is an advance or loan generally taken out on a credit line. Sure you can always ask your boss to advance you some cash, but when related to finance, this normally refers to taking cash from something like a credit card or line of credit.

The interest charges are normally higher on a cash advance, than a normal credit purchase. Rarely is there ever a grace period on interest charges, meaning that the lender does not wait until the end of the month to start charging interest on the advanced cash. These two factor make a cash advance, an expensive option.