What are the two cases required in a recursive function?

What is base case?

Is it necessary to have a base case in a recursive function? Why/Why not?

Identify the base case(s) in the following recursive function:

def function1(n): 
    if n == 0:
       return 5
    elif n == 1: 
       return 8
    elif n > 8 :
       return function1(n-1) + function1(n-2)
    else:
       return -1