"Equalization" (also known as "EQ") is the process of adjusting the high or low tones of a given sound.

Most TVs and playback systems have equalizers built in--even if it's nothing more complicated than a bass or treble control. Anyone who has ever pumped up the bass on a car stereo is already familiar with the basic notion of adjusting equalization.

Consumer playback equipment only allows the adjustment of equalization as it comes out the speakers. Professional equipment, on the other hand, allows the adjustment of the sound's equalization as it's recorded. In other words, in post-production, sounds can permanently be made more treble or bass depending on the needs of the project.