Definition of "pec"

The quest for perfect pecs is so strong that psychiatrists now sometimes refer to it as “bigorexia,” a form of muscle dysmorphia exhibited mostly by men and characterized by excessive weight lifting, a preoccupation with not feeling muscular enough and a strict adherence to eating foods that lower weight and build muscle.

2022 March 5, Alex Hawgood, “What Is ‘Bigorexia’?”, in The New York Times‎