Base: A person who provides support for a top person. The person(s) that holds, lifts, or tosses a top person into a stunt. Must be in direct physical contact with the performing surface. If there is only one person under a top person’s foot, regardless of hand placement, that person is considered a base. A base/athlete in a backbend or inverted position on the performance surface may not be in contact with a top person.
(The definition used in the video is different, but the example shown in the video remains useful)