What and Why?

Equalization is the professional word for "Tone Controls"
Of course it is usually more than just the "Bass" and "Treble" knobs on consumer equipment.

WHAT IS EQUALIZATION (EQ)?
- Tone Controls
  In addition to "Treble" (HF) and "Bass" (LF), professional equipment frequently provides some sort of mid frequency adjustment also, sometimes more than one band.

WHY SHOULD I USE EQ?
- Enhance sound
  To bring out speech (or vocal) from surrounding sound (noise, interference, or accompaniment!)
- Adjust for less than optimal sound pickup
  Certain frequency areas can be boosted (or cut) to counteract bad signal
  Microphone not on-axis, too close (or too far), etc.
- Minimize (or eliminate) interference)
  EQ can sometimes be used to eliminate feedback frequency.
- Reduce noise
  HF (or LF) can be reduced if only noise is present in that area