The term 'chest muscles, informally' can be summarized as 'PECS', which is an acronym for pectoralis major and pectoralis minor. These are two of the four muscles that make up the chest wall, and they are responsible for the movement of the shoulder joint. Pectoralis major is the larger of the two muscles and is located in the upper chest, while pectoralis minor is located in the lower chest. Together, these two muscles help to support the body's posture and provide stability during activities such as lifting and pushing.