Equalization (or EQ) refers to the adjustment of audio frequencies created in beats production, which can either be cut or boosted to reduce or increase the presence of a specific frequency or frequency band. This is usually done to improve the audio aesthetics of your beats.
EQ may be used to eliminate or reduce unwanted sounds and transients, and altering EQ is a good way to adjust the timbre of beats by modifying the substance of its frequencies. This can furthermore assist in fitting beats tracks within the sonic spectrum and overall context of the mix.
Depending on the objective of the project, different EQ units will deliver different tones and character to beats tracks. Some makes will offer slower and smoother frequency contouring, while others can be crisper, sharper and brighter.
Although not an ideal scenario, certain EQs such as the GML 8200 can add a specific sheen in the higher end of the frequency spectrum which can help aid the sound of a low-quality file such as an MP3.