The biceps, commonly thought to be two muscles, are actually comprised of four. The biceps brachii is the muscle that most are referring to when they say "biceps". It has two heads: the biceps brachii: short head (located closest to the body, also known as the 'inner head') and the biceps brachii: long head (located furthest from the body, also known as the 'outer head').
In addition to the biceps brachii, bicep exercises also utilize the brachialis, which surrounds the biceps brachii on both the inside and outside. The coracobrachialis is similar to the short head of the biceps brachii as it runs closest to the body, below the front deltoids, down along the arm.