The full form of AEC is Acoustic Echo Cancellation

AEC is an audio processing effect found in Digital Signal Processors (DSPs) that are designed for audio conferencing, when there is a room with microphones and loudspeakers on the “near side” of a phone or online call as well as someone at the “far side.” The goal of AEC technology is to remove what’s referred to as “acoustic echo,” a byproduct of performing an audio call in a room with microphones and loudspeakers.

One of the key features on DSP units is Acoustic Echo Cancellation (AEC). This feature is not usually found in other types of mixers, and is an absolutely essential function in some situations. AEC is required when a system is used for two-way conversations between locations such as commonly occurs during audio-only phone calls and videoconferences.