But writing? No way.
Now, however, the word carries a great deal of weight and shadows the previous definition. A Beta Reader is one who will take your draft and apply their outside eyes to it. A good one is golden and invaluable to improving a manuscript. Yes they catch spelling and grammar errors (curse you spell-check!), but more importantly they can find things like small plot holes, messy dialogue tags, showing versus telling, and pace issues. Much of what they discover are elements that diminish the story as a whole. Whether it be flow, tempo, or simple "rookie" mistakes, they are problems that the writer often overlooks because they are so close to the work. Betas, however, bring an external viewpoint that is often critical when trying to take a story from decent to excellent.
Granted, there are horror stories from would-be writers about awful or crooked betas and determining the difference between bad and good can be tricky if you don't know the person. A way around this is by cultivating professional friendship in the writing arena. Getting to know others with a similar passion who are willing, able, and most importantly, capable is a big step in the right direction. AW is a great place to look, but they can be found in writing/critique groups, other forums, etc.
A person doesn't need a beta to make a story great, but they are often an invaluable, and free, "service" that I highly recommend. Additionally, it's worth the effort to try your hand at being a beta as well. Not only is critiquing someone else's work an excellent and professional return favor, but it can also help you avoid some mistakes in future endeavors.
Ultimately, betas are some of the greatest unsung heroes of the writing world. They read our slop and then help us polish it into a shine.
And usually for no other reason than the love of writing.
For that, we thank you.
(Indeed, you are.)