WHAT IS THE DIFFERENCE?

Alpha reader (AKA first reader)

They would read an author’s work-in-progress well before it is completed. This could be as early as the first draft, though normally, it is a bit later than that. An Alpha reader would usually identify any significant errors, inconsistencies, or perceived issues with the book, confirming that the overall structure works. This though is changeable from book to book, and would need to be agreed with each author as to what they are looking for.

Beta readers

They would read a book that is close to a finished product. It has normally been self-edited by the author, and is as good as it can be without help from professional editors. It is dependent on the author how in-depth feedback from a Beta reader should be. Sometimes it’s proofing, sometimes its plot error checking. This would be for you to discuss with each author.

ARC readers

An ARC (Advanced Review Copy) reader would read and uncorrected proof (it may have typos as it’s not always a finished product) and they would be expected to write a review on it (posted to at least Amazon and Goodreads). The ARC reader is not expected to give feedback on spelling or grammar—nor should review about those uncorrected issues)