A discriminator is a person who differentiates things or concepts and may act unfairly through prejudice.

A test or variable, etc. that serves to distinguish between different things.

(physics) Any of several electronic devices that convert some property of a signal into an amplitude whose value is proportional to the difference between the value of the input signal and that of a standard.

(marketing) A feature of the seller's offering that differs from a competitor's offering and is important to the buyer in question.