Short for "equalizer." The term is often applied generically as a noun to any sort equalization hardware or software, as well as a verb to the act of changing the equalization curve for a signal.
“I can talk to my Sales Engineer about any piece of equipment, and he always steers me in the right direction. He truly knows what he's talking about, and he never tries to over-sell me on anything. If he worked in the Nashville area, I'd probably owe him about 20 dinners by now!” Michael Erin Woody, Brentwood, TN