Colonization is the act of setting up a colony away from one's place of origin. Remember when the Pilgrims landed at Plymouth Rock? That was the beginning of a period of colonization.
You may have heard of an ant colony, which is a community of ants that decided to set up shop in a particular place; this is an example of ant colonization. With humans, colonization is sometimes seen as a negative act because it tends to involve an invading culture establishing political control over an indigenous population (the people living there before the arrival of the settlers).