Colonialism is a term used to describe the settlement of places like India, Australia, North America, Algeria, New Zealand and Brazil, which were all controlled by the Europeans. Imperialism, on the other hand is described where a foreign government governs a territory without significant settlement. The scramble for Africa in the late 19th century and the American domination of Puerto Rico and the Philippines can be cited as examples of Imperialism.
In Colonialism, one can see great movement of people to the new territory and living as permanent settlers. Though they lead the life as permanent settlers, they still maintain allegiance to their mother country. Imperialism is just exercising power over the conquered regions either through sovereignty or indirect mechanisms of control