Et al. is the shortened form of the Latin phrase "et alia," which means "and others."
The phrase is often used in the title of court cases after one name to represent that there are more persons or organizations involved in the case. In legal citations, when et al. follows an author’s name, it means that more than one author is credited with writing the source being cited.
The persistence of Latin terms like "et al." in modern legal writing is rooted in the influence that Latin had on ancient English legal traditions. Many contemporary legal practices can be traced to their roots in the ecclesiastical courts established by the Roman Catholic Church in Medieval Europe. Latin was the official language of these courts and many common law customs that are still practiced today were developed in Latin.
As a matter of economy of language, the usage of et al. helps to shorten case titles involving many plaintiffs. If, for example, a class action lawsuit involving thousands of consumers was brought against a corporation, the case could be titled "Corporation v. Andrew Alexander, et al." instead of listing every single plaintiff.