"Anglo-Saxons" is a term used to describe the main tribes of Germanic people who invaded Britain beginning in the 5th century AD. The term comes from the names of the two most important tribes, the Angles and the Saxons.
These tribes were Germanic in origin. They came to Britain from the area that is now Denmark and Northern Germany. The tribes had long conducted short raids to plunder the shores of Britain. By the 5th century, though, the Romans were gone and their absence made it possible for the Anglo-Saxons to create permanent settlements. They became the dominant group in Britain until the Normans invaded in 1066.