What qualifies as a class action lawsuit?

In a typical class action, a plaintiff sues a defendant or a number of defendants on behalf of a group, or class, of absent parties, which is a group of people with the same or similar injuries caused by the same product or action. Other names for lawsuits brought by a number of people who suffered similar harm or losses are “mass tort litigation” and “multi-district litigation” (“MDL”). This differs from a traditional lawsuit, where one party sues another party for redress of a wrong, and all of the parties are present in court.