The term 'chest muscle, for short' can be abbreviated in several ways. LAT stands for Latissimus Dorsi, a large, flat muscle located on the back and side of the chest. PEC stands for Pectoralis, a group of muscles located in the chest. PECS stands for Pectoralis Major and Minor, two muscles that make up the pectoralis group. Finally, PECTORALIS is the full name of the pectoralis group of muscles. These muscles are responsible for movements of the arms, shoulders, and chest.