what is a base case in a recursive function python code example

Example: recursion in python

houses = ["Eric's house", "Kenny's house", "Kyle's house", "Stan's house"]

# Each function call represents an elf doing his work 
def deliver_presents_recursively(houses):
    # Worker elf doing his work
    if len(houses) == 1:
        house = houses[0]
        print("Delivering presents to", house)

    # Manager elf doing his work
    else:
        mid = len(houses) // 2
        first_half = houses[:mid]
        second_half = houses[mid:]

        # Divides his work among two elves
        deliver_presents_recursively(first_half)
        deliver_presents_recursively(second_half)