What does Fig.add_subplot(111) mean in Matplotlib?

When you run this code

import matplotlib.pyplot as plt
x = [1, 2, 3, 4, 5]
y = [1, 4, 9, 16, 25]
fig = plt.figure()
fig.add_subplot(111)
plt.scatter(x, y)
plt.show()

Output:

I'm just learning, so I'm following them one by one, but I don't know what 111 is doing ㅜㅜ Sometimes, 212 or something like that comes out. What does that figure.add_subplot() mean?