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. 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. While the subject matter of class action lawsuits may vary, there are two factors that are almost always present:

There are common issues in dispute amongst all members of the class, and
Because there are so many individuals involved, it would make it impracticable to bring them individually before the court.
Depending upon the type of class action, resolution of the lawsuit binds all members of the class certified by the Court.