An alpha reader or beta reader (also spelled alphareader / betareader, or shortened to alpha / beta), also pre-reader, is a person who reads a written work, generally fiction, with what has been described as "a critical eye, with the aim of improving grammar, spelling, characterization, and general style of a story prior to its release to the general public."
The author or writer may use several such readers prior to publication. The terms "alpha" and "beta" are an appropriation from the software industry which uses the terms "alpha" and "beta" for software that are internal works in progress and publicly released tests, respectively (though a "beta" version may still be tested internally, and an "alpha" version may be offered to outside testers in open-source development). While the use of the concept and the term is most common among fan fiction writers, it is growing in popularity with novelists, to the point where some have thanked their beta readers (sometimes even referring to them as such) in their acknowledgments.
Alpha readers are, by definition, the first readers other than the author's own self, and beta readers are at the next stage. The "job descriptions" of alpha and beta readers vary somewhat. An alpha or beta reader, who may or may not be known to the author, can serve as proofreader of spelling and grammar errors or as a traditional editor, working on the "flow" of prose. In fiction, the alpha or beta might highlight plot holes or problems with continuity, characterisation or believability; in fiction and non-fiction, the beta might also assist the author with fact-checking.
Other types of writing groups have been known to use the term critiquer or the abbreviated, informal version critter in the same context as beta reader.