Can I use the term 'abuse' if someone submits five papers to a conference?
Why would you think of it as abuse? If the conference has rules that prohibit it then the author is breaking the rules, otherwise not. The more important question is whether the papers have merit. If they do, all is good. If not, they will be rejected in due course. In the latter case, the committee can admonish the author about a flood of junk. 

The conference program committee doesn't need to accept a lot of papers from an individual and I think in most cases they would like a variety of authors to be represented, but that is their concern. It also seems a valid "policy." 

The committee also needs to be prepared to review, according to their normal methods, all papers submitted. The selection, however, probably involves actually accepting fewer papers than the reviewers approve, just for time and space. 

The "problem" if there is one, will resolve itself. 

If the committee doesn't want this to happen in future, they can write rules into future submission criteria.