A closure relation is a concept in mathematics, particularly in set theory and algebra. It describes a way to extend a set by including all elements that can be derived from it using a specific operation. For example, if you have a set of numbers and a mathematical operation, the closure relation helps identify all possible results of applying that operation repeatedly to the elements of the set. In more formal terms, a set is said to be closed under an operation if performing that operation on members of the set always produces a result that is also a member of the set. For instance, the set of integers is closed under addition, as adding any two integers always results in another integer.