There's no set limit. However, if you want to report a bunch of posts by the same person, or a pattern of posts by the same prson or a thread where many posts are causing a problem (in your view), a better solution is to start a thread in
Moderator Discussions where things can be looked at as a whole picture rather than individual reports.
Also, with spammers, if you see one who has made numerous spam threads, reporting each one is counterproductive. Report one and put in the reason that several have been made. We see them all when we check out the member in question.
Hope this helps.