By beta reading, do you mean beta in a similar sense to software, so like draft reading/readers?
Yep! Basically a beta reader will read a written work (in this case fanfiction) and offer feedback on what can be improved, ranging everywhere from plot to characterization. Though some betas may specialize in only one or two components that go into a good work.
This is a guide for beta reading for original fiction, but the same principles apply!
When I was writing fanfic and had a beta, I sent them a word doc in something Google, and we'd discuss it over Skype.
As Skype is dead, and no one seems to like me using open office, I'd probably just post with no beta.
Which I did do for a long time! I feel they were worse though. More rambling.
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