what is a union in pyton code example

Example: .union in python

set1 = {2, 4, 5, 6}  
set2 = {4, 6, 7, 8}  
set3 = {7, 8, 9, 10} 
  
# union of two sets 
print("set1 U set2 : ", set1.union(set2)) 
  
# union of three sets 
print("set1 U set2 U set3 :", set1.union(set2, set3))