The general tendency for the contracted scope of work to increase, bit by bit.
Can be caused by clients seeking shiny new performance enhancements, especially in acquisition contracting, or by contractor employees gradually doing more than they are required to, especially in services contracting.
Scope creep can lead to contract amendments, formally modifying the performance requirement along with the cost and schedule, or it can lead to an informal (some might say “insidious”) increase in expectations with no corresponding contract coverage or compensation.
See also my comments under Contracting 101
Jim – Yes. 🙂