Recursion

"If you already know what recursion is, just remember the answer. Otherwise, find someone who is standing closer to Douglas Hofstadter than you are; then ask him or her what recursion is."                                                                                                                                                                                                                                 - Andrew Plotkin

Informally defined, recursion is simply the process of repeating self similar elements. The easiest way to visualize a recursive event is by standing in front of a mirror with a mirror. You’ll see an infinite repetition of the same reflection.

In math and computing, recursion is more formally defined.

In mathematics, recursion is a definition of a function in which the application of the function is in its definition. A common example of this is the definition of the fibonacci sequence, which has two properties:

1. The base case or base cases(a non-recursive definition).
2. A set of rules that reduces all other cases to the base case(s).

In computation, a recursive function is one that invokes itself. In most programming languages, the definition of recursive functions end up closely resembling mathematical definitions of recursive functions.