Memoization

Memoization is an optimization technique used primarily to speed up computer programs by having function calls avoid repeating the calculation of results for previously processed inputs. Although related to caching, memoization refers to a specific case of this optimization, distinguishing it from forms of caching such as buffering. A memoized function "remembers" the results corresponding to some set of specific inputs. Subsequent calls with remembered inputs return the remembered result rather than recalculating it. 
http://en.wikipedia.org/wiki/Memoization