Heisenbug is a term used in software programming to describe a computer bug that disappears or alters its characteristics when it is researched.
A common example are bugs that occur in a release-mode compile of a program but do not occur when researched under debug-mode, or some bugs caused by a race condition. The name is a pun on the physics term "Heisenberg Uncertainty principle", which is popularly believed to refer to the way observers affect the observed in quantum mechanics.
In an interview in ACM Queue vol. 2, no. 8 - November 2004 Bruce Lindsay tells of being there when the term was first used and that it was created because Heisenberg said "the more closely you look at one thing, the less closely can you see something else."
See also