A function is like a command that you get to invent and name. It allows us to break our program into smaller parts, making the program easier to understand.
Exits a function, optionally passing back an expression to the caller. A `return` statement with no arguments is the same as `return None`.
Pieces of information you can give to functions when you define them. When the function is called the arguments are the data you pass into the function's parameters. Parameter is the variable in the declaration of the function. Argument is the actual value of this variable that gets passed to the function.
