A more thorough explanation:

Blackletter law refers to the well-established legal rules that are certain and no longer disputable in common law legal structures. It is free from doubt and generally well-known. The term "blackletter" originally refers to the text printed in old law books set in a Gothic type font, which are bold and black. Essentially, it refers to legal concepts that are ancient, important, and indisputable.

Examples of blackletter law include contracts, torts, and land law in English common law. These areas of law consist of mainly technical rules as opposed to areas of the law that are defined by a more conceptual basis. For instance, in contract law, the blackletter law would be the basic elements of a contract, such as offer, acceptance, and consideration. In tort law, the blackletter law would be the basic elements of a tort, such as duty, breach, causation, and damages. In land law, the blackletter law would be the basic rules of property ownership and transfer.

Blackletter law is also known as hornbook law, which refers to the principles and concepts that are usually listed in a student textbook summary of a field. However, blackletter law is characteristically more well-regarded and arcane.