buffer overflow
n. What happens when you try to stuff more data into a buffer (holding area) than it can handle. This may be due to a mismatch in the processing rates of the producing and consuming processes (see {overrun} and {firehose syndrome}), or because the buffer is simply too small to hold all the data that must accumulate before a piece of it can be processed. For example, in a text-processing tool that {crunch}es a line at a time, a short line buffer can result in {lossage} as input from a long line overflows the buffer and trashes data beyond it. Good defensive programming would check for overflow on each character and stop accepting data when the buffer is full up. The term is used of and by humans in a metaphorical sense. "What time did I agree to meet you? My buffer must have overflowed." Or "If I answer that phone my buffer is going to overflow." See also {spam}, {overrun screw}.
bug
n. An unwanted and unintended property of a program or piece of hardware, esp. one that causes it to malfunction. Antonym of {feature}. Examples: "There's a bug in the editor: it writes things out backwards." "The system crashed because of a hardware bug." "Fred is a winner, but he has a few bugs" (i.e., Fred is a good guy, but he has a few personality problems).
Historical note: Some have said this term came from telephone company usage, in which "bugs in a telephone cable" were blamed for noisy lines, but this appears to be an incorrect folk etymology. Admiral Grace Hopper (an early computing pioneer better known for inventing {COBOL}) liked to tell a story in which a technician solved a persistent {glitch} in the Harvard Mark II machine by pulling an actual insect out from between the contacts of one of its relays, and she subsequently promulgated {bug} in its hackish sense as a joke about the incident (though, as she was careful to admit, she was not there when it happened). For many years the logbook associated with the incident and the actual bug in question (a moth) sat in a display case at the Naval Surface Warfare Center. The entire story, with a picture of the logbook and the moth taped into it, is recorded in the `Annals of the History of Computing', Vol. 3, No. 3 (July 1981), pp. 285--286.
The text of the log entry (from September 9, 1945), reads "1545 Relay #70 Panel F (moth) in relay. First actual case of bug being found". This wording seems to establish that the term was already in use at the time in its current specific sense --- and Hopper herself reports that the term `bug' was regularly applied to problems in radar electronics during WWII. Indeed, the use of `bug' to mean an industrial defect was already established in Thomas Edison's time, and `bug' in the sense of an disruptive event goes back to Shakespeare! In the first edition of Samuel Johnson's dictionary one meaning of `bug' is "A frightful object; a walking spectre"; this is traced to `bugbear', a Welsh term for a variety of mythological monster which (to complete the circle) has recently been reintroduced into the popular lexicon through fantasy role-playing games.
In any case, in jargon the word almost never refers to insects. Here is a plausible conversation that never actually happened:
"There is a bug in this ant farm!"
"What do you mean? I don't see any ants in it."
"That's the bug."
[There has been a widespread myth that the original bug was moved to the Smithsonian, and an earlier version of this entry so asserted. A correspondent who thought to check discovered that the bug was not there. While investigating this in late 1990, your editor discovered that the NSWC still had the bug, but had unsuccessfully tried to get the Smithsonian to accept it --- and that the present curator of their History of American Technology Museum didn't know this and agreed that it would make a worthwhile exhibit. It was moved to the Smithsonian in mid-1991. Thus, the process of investigating the original-computer-bug bug fixed it in an entirely unexpected way, by making the myth true! --- ESR]
[1992 update: the plot thickens! A usually reliable source reports having seen The Bug at the Smithsonian in 1978. I am unable to reconcile the conflicting histories I have been offered, and merely report this fact here. --- ESR.]