Recursion - method for determining the class of objects or methods for pre-assignment of one or more (usually simple) his base cases or methods, then the task on the basis of rules defined by constructing a class claiming directly or indirectly on these basic cases.
In other words, the recursion - the way a common definition of the object or action, through himself, using previously defined private definitions. Recursion is used when there are self-challenge.
The definition in the logic of using recursion, is called inductive.