Although there are exceptions, muscles are generally attached to two or more
bones and (when they are active) they affect the movement at joints between
these bones.
It has become conventional to describe one end of each muscle as its origin and the other as its insertion. In a limb, the origin is the more proximal attachment (i.e. nearer the trunk) while the insertion is the more distal attachment (i.e. further from the trunk).
While the origin of limb muscle is usually fleshy, the insertion is frequently
by a relatively inelastic tendon. Some muscles act at both ends of their
attachments, but in general it is the area of insertion which moves most
when the muscle contracts.