Beta Readers VS ARC Readers, what's the difference?
A beta reader is a reader who receives an unedited copy of a manuscript prior to final edits. They provide story feedback and insight on the story ahead of final edits, so that authors can ensure everything is as it should be with a manuscript prior to publication.
ARC readers receive an Advanced Reader Copy prior to publication. This is a manuscript that has been professionally edited and is ready for publication (perhaps with the exception of one or two typos). ARCs are issued in exchange for an honest review to give authors reviews at or ahead of release, because reviews help enormously with a book's visibility.