If we wanted to tell our car to change gear, we tell it not only to change gear, but also which gear to change to. The process of asking these kinds of questions is referred to as passing an argument to the method. An argument (also called a "parameter") is an input value that's provided to a method. An argument can be used to influence: how a method operates on which object a method operates. As one might expect, the object sending the message is called the sender, and the object receiving the message is called the receiver.