Here’s what it is, straight from AO3.
No, it’s not a person. Yes, it’s a collection of abandoned works and, no, they can never be updated because those writers have given up all rights to those works.
If you’re considering giving up on a work, think about the anonymous collection. You won’t be giving up your rights to your work and no one will know you wrote it but it will still exist in fandom and at least be legally and technically linked to you.
Another option for separating the work from your main account is to start another one, share author credit with that account and then remove your original account username as an author, thereby transferring the work and all its comments etc. to the new account.