A graphic equalizer is an audio control device which is often found in middle- and high-end stereo sound systems, or in software for tuning sound in a personal computer. With an equalizer of this kind, you can control (and graphically see) the tone of an audio signal. There are a number of different frequency bands (bandwidths) integrated, each one attached to an amplifier/filter, which go from low frequeny (bass) to high frequency (treble), from the left to the right. You can use it to have more bass, less bass, more treble or less treble for example. Most graphic equalizers have two identical sets of filters/amplifiers, one for the left speaker and one for the right. Typically, the left side starts with 20 Hz going to the right or high end being at 16 kHz. The mid is between 400 Hz and 1.6 kHz.
The “control board” of a graphic equalizer looks like a graphical curve, with slide potentiometers as control buttons.