a proofreader other than the zine editor; used mostly in on-line fiction

A beta reader (sometimes just "beta") is a person who reads a fanfic before it is officially released (i.e. posted on the Web or mailing lists). A beta reader is basically like an editor, checking the story over for mechanical problems (grammar, spelling, punctuation) as well as for things like plot holes, characterization, and all the other stuff we talk about on our Common Errors page. (The term "beta reader" comes from the software world, where software that is ready to be tested by experienced users, but not yet ready to be released to actual customers, is referred to as "beta." Software in even earlier stages of development is called "alpha.") For a complete explanation of why you should always use a beta reader when you're writing fanfic, read Siubhan's essay on betas.

a person who agrees to read and correct fanfictions of other authors

a writer's best friend, and sometimes their biggest foil