A frivolous lawsuit refers to a lawsuit that is brought without justification and has no merit. Such lawsuits are brought by one private party against another. In order for a suit to be considered frivolous under the law, generally there must be no legal grounds for such a suit.
Some people believe that a frivolous lawsuit refers to any silly lawsuit. For example, some might argue that a case in which a person sues McDonald's for the coffee being hot is frivolous, since it may seem silly. In general, however, frivolous lawsuits in the eyes of the law mean something more specific.
Even if a lawsuit is silly, it does not necessarily mean it is without legal merit. For a lawsuit to be classified as frivolous in the eyes of the law, there must be no legal justification for bringing the suit and no possible law on which the suit could be based. It is not frivolous if McDonald's had a legal duty not to make their coffee quite that hot.
When a plaintiff files papers, he must list the facts surrounding the litigation. He must also list the legal grounds, in other words, what law or legal duty is he claiming the facts suggest were breached. Finally, he must list the damages he suffered. The court uses this to determine whether there is a potential legal question and whether it is possible that some duty or law was breached.
If the facts cannot possibly add up to a breach of legal duty, or if there are no legal grounds for a lawsuit, the claim may be considered a frivolous lawsuit. The plaintiff may file frivolous lawsuits for any number of reasons. The plaintiff may wish to hassle or harass the defendant or may truly believe that he has grounds for the suit.
If a defendant is the subject of a frivolous lawsuit, he may be able to sue the other party for the tort of malicious prosecution. In order to win such a case, however, the defendant would need to demonstrate not just that the plaintiff's lawsuit was a frivolous lawsuit and without merit, but also that the plaintiff knew it was frivolous and filed it anyway out of malicious intent.