A tetrad is a group of four related elements or items. In various fields, such as mathematics, biology, and linguistics, tetrads can represent sets of four components that share a common relationship. For example, in genetics, a tetrad refers to a structure formed during meiosis, where four chromatids are aligned. In the context of media theory, Marshall McLuhan introduced the concept of the tetrad of media effects, which examines how any medium influences society through four questions: what it enhances, what it obsolesces, what it retrieves, and what it reverses into when pushed to its limits. This framework helps analyze the impact of different forms of communication.