In the eyes of the law, a "tort" is a civil wrong, as opposed to a criminal wrong. In civil lawsuits based on tort law (also known as personal injury law) plaintiffs must prove that the defendant's bad act, whether intentional or negligent, injured them in some way. Tort or personal injury lawsuits are intended to compensate the injured person instead of punishing the wrongdoer—although in injury lawsuits the wrongdoer is "punished" by having to pay court-ordered compensation (damages) to the injured person.
In contrast, criminal cases are focused on punishment and deterrence, and a crime is considered an offense against society instead of the injured person. For example, an assault is both a tort and a criminal wrong. If someone threatened you and punched you in the face, you could sue them for your personal injuries, and the district attorney could also criminally prosecute them for assault and battery.
There's no universal definition, but typically a "mass tort" civil lawsuit involves many plaintiffs (injured parties) against one or a few defendants (usually corporate manufacturers). Examples of mass tort litigation include:
One high-profile example of a mass tort is lawsuits over the anti-psychotic drug Risperdal, which is apparently very effective in treating adolescent bipolar disorder and autism symptoms, but has also been linked to gynecomastia—a condition causing the enlargement of breast tissue in males. Thousands of young men and their parents have sued Johnson & Johnson (manufacturer of Risperdal) for the significant psychological and physical trauma their families have endured. In late 2019, a jury hit Johnson & Johnson with an $8 billion punitive damages award, although a judge soon cut that figure down to $6.8 million.
A primary benefit of mass tort litigation is economy of scale. Lawsuits are costly, and civil wrongs can go uncompensated when individuals can't afford to prosecute their claims against big corporations alone. In civil litigation, plaintiffs have the burden of proving that the defendant's wrongful conduct caused their injuries (causation) and that their injuries are real (damages).
Because plaintiffs have the burden of proof, the costs of proving these cases can be significant. Mass tort plaintiffs in class actions and multi-district litigation (explained below) benefit from shared research (called "discovery") that their lawyers use to prove that the defendants' wrongful conduct caused their injuries. Highly qualified experts testify in these cases to prove (or refute) the defendants' culpability and the extent of the plaintiffs' damages. The expert witness fees alone could bankrupt anyone who's not independently wealthy. Mass torts provide economy of scale because the costs associated with proving causation are borne by all plaintiffs, as opposed to each plaintiff having to individually prove his or her case.
Mass tort plaintiffs typically live in geographically diverse locations. Consider unreasonably dangerous medications. The manufacturer markets the drug nationwide, and it's possible that consumers in all 50 states will suffer harm as a result. Should each plaintiff file an individual lawsuit, the court system would be overwhelmed with hundreds or thousands of cases with the same or very similar underlying facts. That scenario inspired the advent of modern-day mass tort litigation.
Mass tort lawsuits include class actions and multi-district litigation (MDL). Each system is designed to provide an efficient vehicle for resolving multiple claims against the same defendant, but they are structured differently. A class action is a single lawsuit that binds every potential claimant (except those who "opt out"), even if they never join the lawsuit or get a check. MDL, on the other hand, involves many lawsuits based on the same facts. These cases are consolidated and sent to the MDL, where part of the case (general causation) is proved on behalf of all plaintiffs.
MDLs require each plaintiff to file a claim, as opposed to a class action, where one claim is filed on behalf of the entire class and binds everyone. Also, MDL settlements don't apply globally to potential plaintiffs, only to those who file claims.
The similarity of damages is often what determines whether a case will be litigated as a class action or MDL. In class actions, the damages are so similar that "class representatives" can prosecute the litigation for the entire group. On the other hand, MDLs require separate proof of each plaintiff's damages. MDL is usually better for plaintiffs than class actions because the damages awards are higher. In a class action, each plaintiff receives the same percentage of the entire award, but in MDLs, each plaintiff is awarded damages based on their own provable injuries.
If you or a loved one has suffered the kind of harm that might give rise to a mass tort claim, you might want to discuss your situation (and your options) with a personal injury lawyer.