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.