The word bug has a number of possible interpretations in English. It is usually used colloquially to denote very small animals (such as insects, spiders, snails, slugs, etc). From this meaning stem many others.
When used to denote animals, a bug is often and incorrectly used in vernacular to refer to any small, terrestrial arthropod, sometimes taken to include creatures like snails and slugs as well. Since such insects are often irritating and frustrating (mosquitoes, flies and cockroaches being prime examples of such), this word has also come to refer to something which is irritating or frustrating. For instance, a person might say someone (or a problem) is "bugging" (irritating or frustrating) them.
A bug is, however, a precise scientific term that refers to insects of the orders Hemiptera and Homoptera.
The term bug is often used in a computer context. It describes unwanted behavior of a computer program or electronic device. More specific terms are failure or defect. See computer bug (including origin of the usage) or debugging.
Since it refers to small animals, the term bug is also occasionally (and inaccurately) used to refer to microscopic life forms. Somebody might refer to have caught the "pneumonia bug", for instance.
A further extension of this meaning is to small surveillance devices. This can be seen as an extension of the existing meaning of something which is small and irritating (the possible presence of surveillance bugs acts as a detriment to free speech in any context). Alternatively, a bugging device could also be likened to a "fly on the wall" - another kind of bug. See bugging.
Bug is also the name of two rivers in eastern Europe, the Western and Southern Bug. See Bug (rivers).
In gambling jargon, a bug is a small holdout device that can secretly be attached at the under side of the card table for the purpose of cheating. A card cheat will use a bug to conceal extra cards under the table for further use.
In some variants of poker, the bug is a restricted wild card, which can either represent an ace or fill a gap in a straight or flush.
In a flight instrument, a bug is a manually positioned marker or pointer which is set to remind the pilot where the needle on the instrument should be pointing. This helps her avoid the need to hold settings in her head, and can then just fly to keep the needle aligned with the bug. The term may have arisen because of the superficial similarity to the appearance of an insect.
A bug is also a name for a special kind of morse code key originally manufactured by the Vibroplex company.
