Earlier in this chapter, you learned how to use variables outside of stored procedures. Variables can also be used inside a stored procedure, mainly with flow control statements. When working with stored procedures, you may want to pass in a value to use inside the stored procedure. This is called a parameter. The main difference between a variable and a parameter is that parameters are static throughout the procedure, but a variable can be changed during the stored procedure. IN parameters allow you to provide a value or values to the stored procedure. OUT parameters allow you to receive output from the stored procedure.