I
Coding error in a computer program that prevents it from functioning as designed.
Most software companies have a quality-assurance department which is charged with finding program bugs while the program is in development (debugging); bugs are also often detected by means of beta testing (testing of a product, often by potential consumers, before it is placed on the market). The term originated in a computer context in 1945 when a moth flew into and jammed an electrical relay of the Harvard Mark II computer; it was extracted and taped into the log book with the inscription "First actual case of bug being found" (the term having previously been used for other kinds of mechanical defects).
II
Commonly, any insect ; scientifically, any member of the insect order Heteroptera.
In scientific usage, when the word "bug" is part of the common name for a member of the order Heteroptera, it is a separate word (e.g., "chinch bug"); when used as part of the common name for an organism that is not a heteropteran, it is not separated (e.g., the ladybug, in the order Coleoptera). In common usage, there are many exceptions to this convention (e.g.,
III
[c mediumvioletred] (as used in expressions)
lightning bug
assassin bug
Bug River
Western Bug River
potato bug
June bug
pill bug
sow bug
squash bug
leaf footed bug
Y2K bug
{{link=millennium bug">millennium bug
Year 2000 bug