"MUST" is a modal verb used to express obligation or necessity. When someone says they "must" do something, it means that it is required or essential. For example, if a teacher says students "must" submit their assignments by Friday, it indicates that meeting this deadline is mandatory. In everyday life, "must" can apply to various situations, such as rules, laws, or personal commitments. For instance, drivers "must" obey traffic signals to ensure safety on the road. Similarly, employees "must" follow company policies to maintain a productive work environment.