Definition of Mission Creep

What does the term "mission creep" mean? What is the definition of the term "mission creep"?

In the third Presidential debate of the 2012 election cycle, Mitt Romney and Barack Obama used the term "mission creep" when discussing the situation in Libya.

Definition of MIssion Creep - Financial Dictionary - Politics - Army
Let's take a look at a fictional example to fully illustrate the term "mission creep":

The United States and Great Britain decide to jointly enforce a "no-fly zone" over a Middle Eastern country. This is the primary objective of the mission.

Fighting between the leadership of the fictional country and rebels flares up while the US and UK are enforcing the "no-fly zone". The United States and the United Kingdom release a joint statement in which they proclaim that it is time for new leadership in the country, and that the current leadership must fall. This leads to some criticism as some people claim that the statement means that the United States will get drawn into the fighting, which will lead to "mission creep". In other words, the United States will surpass their original objectives of just enforcing the "no-fly zone" and will instead get drawn further into the conflict.

-- Articles That Mention Mission Creep: