An imperative sentence is a type of sentence that gives a command, instruction, or request. It often starts with a verb and can be directed at one person or a group. For example, "Close the door" or "Please pass the salt" are both imperative sentences. They can end with a period or an exclamation mark, depending on the tone. Imperative sentences can also imply the subject "you," even if it is not explicitly stated. For instance, in the sentence "Sit down," the subject is understood to be "you." This makes imperative sentences unique in their directness and clarity in communication.