In measure theory (a branch of mathematical analysis), one says that a property holds almost everywhere if the set of elements for which the property does not is a null set.

If used for properties of the real numbers, the Lebesgue measure is assumed unless otherwise stated. (The Lebesgue measure is complete.)

Occasionally, instead of saying that a property holds almost everywhere, one also says that the property holds for almost all elements. The term almost all in addition has several other meanings however.

Here is a list of theorems that involve the term "almost everywhere":