In a nutshell, a beta reader is someone in an author's target audience who reads a book while it's still in the manuscript "beta" stage, to let an author know if they like it.
Beta readers let an author know whether or not an idea is worth pursuing by letting them "test the waters" with real readers from their real target audience and get feedback from them on the work. Because the feedback is coming from the same pool of people who are likely to buy your book, the feedback will be generalizable to the entire target audience! That means that you can use the feedback from beta readers to create not only a book that they enjoy, but a book that will reach more people once it's published!
Beta readers are supposed to represent real readers, so they need to actually be part of the target audience, because they can give all kinds of feedback that would be helpful to the author! They can let an author know how they feel about characters, settings, plot, pacing, anything that has to do with their reading experience. Remember, the goal is for the author to get experience from real readers! In my case, I'm currently story editing, so I'm looking for big picture things, but everything helps!
The book I'm currently editing, The Crimson Mage, has an adult target audience in the fantasy genre.
Target audiences are typically made up of a reading level based on age and the genre fandom. The ranking for age are: "picture, learn-to-read, preschool, children, middle grade, teen, young adult, and adult". Some scales also use a category called "new adult" between "young adult" and "adult", but I'm going to be real- I do not understand what that category is. Some lists include it and some don't, and my ignorance means that The Crimson Mage may actually be New Adult fantasy.
First of all, if you do that, I'll love you forever.
But secondly, I'm not sure if I've done this right or not. If I have, a comment box will show up under every chapter and you should be able to post. If you want to just talk to me, you can also hit me up on discord, found on the main page.
I'm really hoping that the comment boxes load. Wish me luck!