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: Admiral Grace Hopper (an early computing pioneer
better known for inventing COBOL) liked to tell a story in
which a technician solved a 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 (NSWC). 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),
The text of the log entry (from September 9, 1947), reads "1545
Relay #70 Panel F (moth) in relay. First actual case of bug being
found". This wording establishes 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 a more specific and rather
modern use can be found in an electrical handbook from 1896
("Hawkin's New Catechism of Electricity", Theo. Audel & Co.)
which says: "The term `bug' is used to a limited extent to
designate any fault or trouble in the connections or working of
electric apparatus." It further notes that the term is "said to
have originated in quadruplex telegraphy and have been transferred
to all electric apparatus."
The latter observation may explain a common folk etymology of the
term; that it came from telephone company usage, in which "bugs in
a telephone cable" were blamed for noisy lines. Though this
derivation seems to be mistaken, it may well be a distorted memory
of a joke first current among telegraph operators more than
a century ago!
Or perhaps not a joke. Historians of the field inform us that the
term "bug" was regularly used in the early days of telegraphy to
refer to a variety of semi-automatic telegraphy keyers that would
send a string of dots if you held them down. In fact, the
Vibroplex keyers (which were among the most common of this type)
even had a graphic of a beetle on them (and still do)! While the
ability to send repeated dots automatically was very useful for
professional morse code operators, these were also significantly
trickier to use than the older manual keyers, and it could take
some practice to ensure one didn't introduce extraneous dots into
the code by holding the key down a fraction too long. In the hands
of an inexperienced operator, a Vibroplex "bug" on the line could
mean that a lot of garbled Morse would soon be coming your way.
Further, the term "bug" has long been used among radio technicians to
describe a device that converts electromagnetic field variations into
acoustic signals. It is used to trace radio interference and look for
dangerous radio emissions. Radio community usage derives from the
roach-like shape of the first versions used by 19th century physicists.
The first versions consisted of a coil of wire (roach body), with the two
wire ends sticking out and bent back to nearly touch forming a spark gap
(roach antennae). The bug is to the radio technician what the stethoscope
is to the stereotype medical doctor. This sense is almost certainly
ancestral to modern use of "bug" for a covert monitoring device,
but may also have contributed to the use of "bug" for the effects
of radio interference itself.
Actually, use of `bug' in the general sense of a disruptive event
goes back to Shakespeare! (Henry VI, part III - Act V, Scene II:
King Edward: "So, lie thou there. Die thou; and die our fear; For
Warwick was a bug that fear'd us all.") 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."
A careful discussion of the etymological issues can be found in a
paper by Fred R. Shapiro, 1987, "Entomology of the Computer Bug:
History and Folklore", American Speech 62(4):376-378.
[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, but due to
space and money constraints was not actually exhibited years
afterwards. Thus, the process of investigating the
original-computer-bug bug fixed it in an entirely unexpected way,
by making the myth true! --ESR]