What is "heisenbug"

n. (context computing English) A software bug which fails to manifest itself during debugging; a problem that cannot be diagnosed in the debugger because it does not occur in that environment.

In computer programming jargon, a heisenbug is a software bug that seems to disappear or alter its behavior when one attempts to study it. The term is a pun on the name of Werner Heisenberg, the physicist who first asserted the observer effect of quantum mechanics, which states that the act of observing a system inevitably alters its state. In electronics the traditional term is probe effect, where attaching a test probe to a device changes its behavior.

Similar terms, such as bohrbug, mandelbug, and schrödinbug have been occasionally proposed for other kinds of unusual software bugs, sometimes in jest; however, unlike "heisenbug", they are not widely known or used.