So What do the words Alpha, Beta and Omega have in common? Well, they're all Greek letters and that's why it sounds like a frat or sorority. As it relates to writing, you could call it the fraternal order of readers.
It's important to know the difference between these three types and their respective roles.
These are the people that read and comment on your story as you are writing it. Most likely your critique group. Alphas are super important, because its always good to have extra pairs of eyes on your plot line to point out any major holes. Better to find them in the early stages of crafting than when you are 300 pages strong and then realize you took a wrong turn on page 50.
This is who you farm your book out to after you are done with the first draft and maybe a round of revisions. It's good to have a mix of author buds and non writing folk. The author type people will pick up some of the structuring nuances you might have mixed, but it's important to have a beta or two from your target audience. Remember, when your story gets published, not all of your readers will be writers. The things that may drive another author nuts, will be loved by the general public. It's good to have a wide sampling to see what works and what doesn't. And that's what a good general Beta is for. They're not line editors -- not there to fix your commas. They will point out some macro things. Perhaps whether or not they liked your characters, or maybe were confused by a plot point. Pacing is a good thing to ask about.
This is a very exclusive club. It consists of you and your agent or editor. After all, you and whoever might be paying you for a story, are the end of the line. This is when you reread all the Betas commentary and decide whether you want to use it or not. The opinion of an Omega reader will probably hold the most weight. It's one thing if the neighbor down the street tells you you need to rewrite an entire scene. It's a whole different kettle of popcorn when an agent tells you to.
So there you have the basics of the fraternal order of readers. Are you a member?