A beta does much more than just read. In many ways, they are both a proofreader and an editor. Their job is to catch typos and other technical errors from misspellings to the wrong use of homophones (ie peaked rather than peeked). They also provide feedback to the author about the post though they do not edit it per se.
Whether or not the word beta ever passes your lips or fingertips, a beta is someone every blogger can use. It’s amazing the difference another pair of eyes can make when it comes to providing quality content for your blog. In fact, a beta should go hand in hand with spellcheck, grammarcheck and your SEO assessment.
Why not just call them a proofreader or editor?
For many bloggers, especially those just beginning their blogging career, beta sounds less intimidating than either Editor or Proofreader. Also, both editors and proofreaders are professional titles which implies they would like to be paid for their services. Beta stems from RP and fanfic and while some betas are very talented and extremely good at what they do, they are not always paid. In fact, if you are friends with another blogger you might want to ask them if they will be your beta and volunteer to be there’s, just remember, you may have to explain it first!