Idempotence (UK: / ˌ ɪ d ɛ m ˈ p oʊ t ən s /, US: / ˌ aɪ d ə m-/) is the property of certain operations in mathematics and computer science whereby they can be applied multiple times without changing the result beyond the initial application. The concept of idempotence arises in a number of places in abstract algebra (in particular, in the theory of projectors and closure operators.

An idempotent HTTP method is an HTTP method that can be called many times without different outcomes. It would not matter if the method is called only once, or ten times over. The result should be the same. It essentially means that the result of a successfully performed request is independent of the number of times it is executed.

Idempotent methods. An idempotent HTTP method is a HTTP method that can be called many times without different outcomes. It would not matter if the method is called only once, or ten times over. The result should be the same. Again, this only applies to the result, not the resource itself.

In computing, an idempotent operation is one that has no additional effect if it is called more than once with the same input parameters. For example, removing an item from a set can be considered an idempotent operation on the set. In mathematics, an idempotent operation is one where f(f(x)) = f(x).