Give me a simple summary of idempotency

Context: Idempotence 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 and functional programming.

The term was introduced by American mathematician Benjamin Peirce in 1870 in the context of elements of algebras that remain invariant when raised to a positive integer power, and literally means " the same power", from idem + potence.

Answer: Idempotency is a mathematical property where if you apply an operation multiple times, the result remains the same -- just as if you had only applied the operation once. Idempotency can grant you at-most-once semantics.