In computer programming, a magic cookie or cookie is a token or short packet of data passed between communicating programs, where the data is typically not meaningful to the recipient program. 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. The cookie is often used like a ticket - to identify a particular event or transaction.

For example, when one visits a website, the remote server may leave a cookie on one's computer, see HTTP cookie.

Video terminals

Some early video terminal units did not have the memory capacity to store video attributes (such as intensity or inverse display) for each on-screen character individually. Instead, a "magic cookie" character was inserted that displayed as a blank but instructed the video logic to change the attribute of subsequent text. As a consequence, each shift of display attributes would invariably insert one or more space characters, which had to be taken into consideration when designing a particular screen layout. Videotex, as used in teletext, is one of the few instances which have survived into the modern era.

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