The Rice University Neologisms Database

Etymology : Clipping from the term “beta read,” which then was clipped and converted into a past tense and past participle form with the addition of the inflectional suffix ‘ed’. The term “beta” was previously used to mean secondary viewer or the second stage of a product release cycle, in which users other than the creators are recruited to evaluate the product. Beta is used to mean secondary because of its position as the second letter in the Greek alphabet, after Alpha.