noun

• (sports) A goal, run, point, etc. that equalizes the score.
  "[Bendtner was central to it at all, firstly firing home, via a deflection off Gareth McAuley, after being teed up by Sebastien Larsson's neat backheel, and then a minute later crossing for Elmohamady to head in an equaliser."
• (music, electronics) An electronic audio device for altering the frequencies of sound recordings.
  "Several digital effects are supported by Deck, ranging from a digital equalizer, which lets you accentuate or attenuate certain frequencies, to a stereoizer, which processes a mono- phonic recording to simulate stereo."
• (mathematics) A set of arguments where two or more functions have equal values; the solution set of an equation.
• (category theory) A morphism whose codomain is the domain of a parallel pair of morphisms and which forms part of the limit of that parallel pair. Equivalently, a morphism which equalizes a parallel pair of morphisms in a limiting way, which is to say that any other morphism which equalizes that parallel pair factors through this limiting morphism; and moreover such factorization is unique.