Noun

Form of invasion, dispossession and subjugation of a people. The invasion need not be military; it can begin—or continue—as geographical intrusion in the form of agricultural, urban, or industrial encroachments. The result of such incursion is the dispossession of vast amounts of lands from the original inhabitants. This is often legalized after the fact. The long-term result of such massive dispossession is institutionalized inequality. The colonizer/colonized relationship is by nature an unequal one that benefits the colonizer at the expense of the colonized. 

Colonialism is similar but not the same as imperialism, which is a policy of extending a country's power and influence through diplomacy or military force. Colonialism is a type of imperialism.

Source

Adapted from Southern Jamaica Plain Health Center and Colonization and Racism Film by Emma LaRocque