An intermittent fault, often called simply an "intermittent"[citation needed] (or anecdotally "interfailing"[citation needed]), is a malfunction of a device or system that occurs at intervals, usually irregular, in a device or system that functions normally at other times.
An intermittent fault is caused by several contributing factors, some of which may be effectively random, which occur simultaneously.
[1] Intermittent failures can be a cause of no-fault-found (NFF) occurrences in electronic products and systems.
For example, a hard drive supplier claimed NFFs were not failures and allowed all NFF products to be returned to the field.
In computer software a program may (cause 1) fail to initialise a variable which is required to be initially zero; if the program is run in circumstances such that memory is almost always clear before it starts, it will malfunction on the rare occasions that (cause 2) the memory where the variable is stored happens to be non-zero beforehand.