Said another way, a recurrence relation is a function that is defined in terms of itself. For example, a function to generate the fibonacci numbers mentioned by artermis entreri above is defined as:

general case:

F(n) = F(n - 1) + F(n - 2), for n > 2

base cases:

F(1) = 1

F(2) = 1

One use of recurrence relations is in determining the complexity of algorithms.