A procedure is able to call other procedures from inside it. It is also able to call itself from inside it. This is known as Recursion.

Procedure Recurse()
Recurse
End Proc

This procedure repeatedly calls itself. This, however, would cause an infinite loop because it would just keep calling itself and would never stop.

In order to prevent this from happening recursive procedures need to be able to keep track of how many times they have been called.

Procedure Recurse(n)
if n>0
Recurse(n-1)
end if

This would only call the procedure n times because each time it is called the value of n is reduced. Once n becomes less than or equal to 0, the procedure is no longer called and termination of all the called procedures would begin.