Overcommit

Overcommit refers to the practice of giving out virtual memory with no guarantee that physical storage for it exists. To make an analogy, it's like using a credit card and not keeping track of your purchases. A system performing overcommit just keeps giving out virtual memory until the debt collector comes calling — that is, until some program touches a previously-untouched page, and the kernel fails to find any physical memory to instantiate it — and then stuff starts crashing down.