A colonist is a member of a government-backed group that settles in a new country or region. The land that's claimed by a colonist is usually already occupied by another group of people.
A colonist can also be called a settler, someone who helps start a settlement in a new land. You might think of colonial America and the original colonists, British subjects who settled along the eastern seaboard and claimed the land as their own, despite the presence of native people. Throughout history, colonists have tended to come from Western countries. At the heart of the word colonist is the Latin root colere, "to inhabit, tend, or guard."