Oh man, I feel kind of old now… Is this term not in popular use anymore? XD

Beta-reading is like the amateur version of an editor–someone who reads someone else’s piece of writing and gives their opinions on it as a reader. It’s a little bit different from copy editing (which is more like proofreading) in that the beta-reader is usually looking not just for technical errors but for general, overall issues such as places where the pacing feels off, the characters aren’t quite right, the story starts to feel a bit boring, etc.

It used to be fairly common practice to have a beta-reader if you were a fanfic author, just so that you’d have someone to read over your stuff before you posted it, but I don’t know if that’s still a thing nowadays?