A more thorough explanation:

A vexatious litigant is someone who repeatedly files frivolous lawsuits. This means that they file lawsuits that have no legal basis or merit, and are often done to harass or annoy the other party.

Many jurisdictions have laws or rules that require a vexatious litigant to get permission from the court before filing any further lawsuits or legal documents. This is to prevent them from wasting the court's time and resources, as well as the time and resources of the other party.

• John has filed five lawsuits against his former employer, all of which have been dismissed by the court. The court has now declared him a vexatious litigant and he must get permission before filing any further lawsuits.
• Sarah has filed multiple lawsuits against her neighbor for trivial matters, such as the color of their house or the type of plants in their garden. The court has deemed her a vexatious litigant and she must get permission before filing any further lawsuits.

These examples illustrate how a vexatious litigant repeatedly files lawsuits that have no legal basis or merit, causing unnecessary burden on the court and the other party.