A more thorough explanation:

A mass tort is a legal action that involves numerous individuals who have been harmed or injured by the same act or omission. This can include events such as explosions, commercial plane crashes, groundwater contamination due to toxic waste disposal, or noxious pollution from industrial factories.

Mass tort actions are not single cases, but rather groupings of individual lawsuits that allege the same issues against the same defendant(s). These actions are used to seek remedies in situations where a class cannot be certified or there exists some benefit over filing a class action lawsuit.

For example, if a company's toxic waste disposal contaminates the groundwater in a community, causing numerous individuals to suffer health problems, each individual may file a separate lawsuit against the company. These individual lawsuits would be grouped together as a mass tort action.

Mass torts can also give rise to mass tort class action lawsuits, where a complaint from a class representative, a person representing a class of injured individuals, is heard in one suit by federal courts under Rule 23 of the Federal Rules of Civil Procedure, so long as the involved parties establish minimal diversity.

Another example of a mass tort is the litigation against the manufacturers of the drug Vioxx. The drug was found to increase the risk of heart attacks and strokes, and thousands of individuals filed lawsuits against the manufacturers. These individual lawsuits were grouped together as a mass tort action.