A graphic equalizer is, as the name implies, an equalizer which uses a graphical layout to represent the changes made. It uses a series of sliders (usually vertical) which correspond to a set of fixed frequency bands. You raise or lower each slider to boost or lower (attenuate) the level of that frequency band.
Graphic equalizers are commonly referred to by the number of bands (e.g. 51-band, 31-band) or by the frequency separation of each band expressed in octaves (e.g. 2/3 octave, 1/3 octave, 1/6 octave).