what does the floor function do in python code example

Example 1: python floor

import math
x = 3.86356
math.floor(x)
#Returns: 3
math.ceil(x)
#Returns: 4

Example 2: floor python

def floor(k,b):
  return b-k%b+k-b

print(floor(3,10)) # Prints: 0
print(floor(7.94,2.125)) # Prints: 6.375