Cash usually refers to money in the form of currency, such as bills or coins. Cash can also refer to checks, money orders, cashier's checks, bank drafts, or traveler's checks. In all these forms, the term indicates the most liquid form of assets, which have a fixed value and can be easily converted to currency. "Cash pay" (as opposed to, e.g., stock options) would almost always be in the form of a check or bank deposit — but the employee can easily get cash per se from the bank.
As a verb, "to cash" an item (such as a check) denotes exchanging the item for cash.
