1. A handle, transaction ID, or other token of agreement between cooperating programs. "I give him a packet, he gives me back a cookie".

The claim check you get from a dry-cleaning shop is a perfect mundane example of a cookie; the only thing it's useful for is to relate a later transaction to this one (so you get the same clothes back).

Another example is an HTTP cookie.

Compare magic cookie; see also fortune cookie.

2. A cracker term for the password list on a multi-user computer.

3. An adjective describing a computer that just became toast.