I'm doing a beta-read. Well written, great ideas, etc. Unfortunately, the book is turning out to be much darker than I'm comfortable with. I'll probably try to get to the halfway point before deciding to give up.
Like alpha, beta, gamma readers. Used by authors to get feedback at various stages of their book before it is published. Alpha stage is very rough, like first draft. Not sure where the line lies between beta and gamma stage, but they are close to finished works - only typos and minor changes would be made based on reader feedback.
For indie authors, beta readers often help to get a few reviews out close to book publication.
I'm a bit active on book-related forums. I post reviews of books I've read, give book recommendations, etc. In this case, the author contacted me based on my reviews.