The cookie is often used to identify a particular event or as "handle, transaction ID, or other token of agreement between cooperating programs".
The contents are opaque and not usually interpreted until the recipient passes the cookie data back to the sender or perhaps another program at a later time.
[citation needed] In some cases, recipient programs are able to meaningfully compare two cookies for equality.
[citation needed] The term magic cookie appears in the man page for the fseek routine in the C standard library, dating back at least to 1979, where it was stated: An analogy is the token supplied at a coat check (cloakroom) counter in real life.
Cookies are a component of the most common authentication method used by the X Window System.