I've talked about sending my books out to "betas" before. If you've been scratching your head, thinking, "Why is she sending out a story to a FISH?!" Ha. No, a "beta" refers to a "beta reader" as in one of those test people who...tests...things. Like computer programs. Or books!
I have a handful of close friends who love to read and give great feedback on my stories. They've read Book One and Book Two which I SO SO SO appreciate. I need to make sure that what I said in Book One carries over to Book Two. That things make sense. That characters are true to what I've written before. That I don't have any plot holes. All those things that readers will catch if you mess up.
If you are a writer and DON'T have a beta reader or a critique partner, I'd ask you, "Why not??" I know that it's scary to put yourself out there by letting someone else read what you've labored over. But if you can't let a friend read it, how are you going to let the public at large read it????
There a LOTS of places to find a critique partner (CP). Look online or ask a friend that reads the genre that you write in. Be open to hearing criticism about your story.