Vexatious litigation is that which is brought, regardless of its merits (usually it has none) solely to harass or subdue an adversary. It may take the form of a primary frivolous lawsuit or may be the repetitive, burdensome and unwarranted filing of meritless motions in a matter which is otherwise a meritorious cause of action. It is an abuse of the judicial process and almost always brings down sanctions on the offender.
Repeated and severe instances by a single lawyer can result in his disbarment.
See also barratry.