Basically, it's when an account has been sold/traded so many times it has caught aids. Like someone having intercourse loads of times with loads of different person, could catch aids.
People on the Internet use the term 'aids' for accounts/items on the Internet that have been passed around alot to multiple people.
Say for example that someone had an instagram account username, and that username has been owned by five or more owners, then that said username would be declared to have aids.
If you have anymore questions, or would like a more in-depth explaination just let me know.