Function creep
FUNCTION CREEP, sometimes referred to as "functionality creep", is what occurs when an item, process, or procedure designed for a specific purpose ends up serving another purpose for which it was never planned to perform.
Terminology Debate
"Function creep" is the preferred term rather than "functionality creep". The definitions, as given by dictionary.com, and the 37,800 hits for "function creep" on Google versus the 2,680 Google hits for "functionality creep" back up this assertation. So, in the interest of making knowledge available to eveyone, refer to the subject of this page as "function creep". Otherwise, the issue will be made muddier by trying to redefine or invent terms.