PEC can refer to different things depending on the context. Here are some possible meanings:

1. Certified email: PEC stands for "posta elettronica certificata" in Italian, which means "certified email". It is a special type of email used in Italy, Switzerland, Hong Kong, and Germany that provides a legal equivalent of traditional registered mail. Certified email allows users to legally prove that a given email has been sent and received, and to guarantee the identity of the sender and the recipient, the date and time of sending and receiving, and the content of the message.

2. Pectoral muscle: PEC is an abbreviation for the pectoral muscle, which is a muscle connecting the ventral walls of the chest with the bones of the upper arm and shoulder. It is also known as the "pecs" and is often associated with bodybuilding and fitness.

3. Picture Exchange Communication System: PECS stands for "Picture Exchange Communication System". It is a modified applied behavior analysis program designed for early nonverbal symbolic communication. The PECS approach uses pictures or symbols to help individuals with communication difficulties to express their needs and wants, and to interact with others. The program consists of six phases and begins by teaching an individual to give a single picture of a desired item or action to a "communicative partner" who immediately honors the exchange as a request. The system goes on to teach discrimination of pictures and how to put them together in sentences. The primary goal of PECS is to teach functional communication.

In summary, PEC can refer to certified email, the pectoral muscle, or the Picture Exchange Communication System.