What does & in Python mean?

Good evening to everyone! Please tell me what the operator & in Python means? (this is not related to many).
for example, there is a code that checks whether a number is a power of two:

  n =  int  ( input  ())   if  n & (n -  1 ):   print  ( '" this number is not a power of two' )   else :   print  ( is the number - a power of two' )   

what does n & (n-1) mean in the second line?