/P-C-i-zəm/
n. A piece of code or coding technique that takes advantage of the unprotected single-tasking environment in IBM PCs and the like, e.g., by busy-waiting on a hardware register, direct diddling of screen memory, or using hard timing loops.
Compare ill-behaved, vaxism, unixism. Also, 'PC-ware' n., a program full of PC-isms on a machine with a more capable operating system. Pejorative.