Little lapses of attention or (in more severe cases) consciousness, usually brought on by having spent all night and most of the next day hacking. "I need to go home and crash; I'm starting to get a lot of parity errors." Derives from a relatively common but nearly always correctable transient error in memory hardware. It predates RAM; in fact, this term is reported to have already have been in use in its jargon sense back in the 1960s when magnetic cores ruled. Parity errors can also afflict mass storage and serial communication lines; this is more serious because not always correctable.
[glossary]