Definition - What does Joinder mean?
A joinder is when multiple parties are grouped together in a lawsuit. When a joinder occurs, multiple parties act as either co-plaintiffs or co-defendants. This can happen when the different parties are both being held liable for a crime or a tort, or when the different parties both have a cause of action in the same suit.
Justipedia explains Joinder
The reason why joinders are often used in court proceedings is because they can save a significant amount of time, and they are more efficient. For example, if a person is suing a manufacturer and a trucking company over the same issue, then it is generally less time-consuming to have the two companies form a joinder, and act as co-defendants in one trial, versus having two individual trials.
Joinders can be used for a wide variety of cases.