Everyone And Their Mother Meaning

(idiomatic) A large number of people; most people.

Example: 2011, "Now Everyone And Their Mother Is Shorting China, Especially These Four Stocks", Business Insider
2007, Hot Fuzz
  DS Andy Wainwright: You do know there are more guns in the country than there are in the city.
  DS Andy Cartwright: Everyone and their mums is packin' round here!