Definition:Friction

Definition
Friction is a force whose tendency is to reduce the velocity of a body relative to its surroundings.

It is caused by interaction of the matter in the body with that of the environment in which it is traveling.

Friction is (at a fundamental level) an electromagnetic force.

That is, bits of the medium in or on which the body is traveling get in the way (on a molecular level) of bits of the body.

The less friction, the less the reduction in velocity.

If there were no friction, then motion would continue for ever.