The hexadecimal word-fill pattern for freshly allocated memory under a number of IBM environments, including the RS/6000. Some modern debugging tools deliberately fill freed memory with this value as a way of converting heisenbugs into Bohr bugs. As in “Your program is DEADBEEF” (meaning gone, aborted, flushed from memory); if you start from an odd half-word boundary, of course, you have BEEFDEAD. See also the anecdote under fool and dead beef attack.