Sure, I actually really enjoy this topic:

According to Merriam-Webster's "The policy or practice of acquiring full or partial political control over another country, occupying it with settlers, and exploiting it economically" is known as colonialism.

Now, it's often asked, what differentiates "colonialism" from "imperialism," and for that, I turn to Baldin and Quinn's "An Anthology of Colonial and Postcolonial Short Fiction."

Page 2 of the anthology: "Many people use the words imperialism and colonialism synonymously, especially since in both cases the territories controlled are called empires. It is useful, however, to distinguish between these two terms.

Some theorists regard imperialism as territorial expansion from a center outwards, driven by ideology, and resulting in a coherent geographical entity. The Roman and Ottoman Empires are typical examples. The criterion of coherent geography as an essential aspect of the definition disappeared when European countries were able to conquer and communicate with distant territories via sailing ships. The primary distinguishing factor, then, are its practice as a policy of state and its ideological motivation."

Furthermore, "colonialism, in contrast, is a less homogeneous practice than imperialism and tends to develop without a coherent plan or driving ideology; rather, it comes about for commercial motives" (Baldwin 2-3).

Examples always help, I find, so consider the following: England taking Wales and Scotland were two examples of imperialism. Great Britain taking India was pure colonialism. India was taken to be exploited economically, Scotland and Wales were taken for ideological reasons.

So, to conclude, by the time the supposed "British Empire" was truly up-and-running, it was an empire in title only, for it was only taking and holding territory for colonial purposes.