英语谜语Tom wanted to pay for his meal at the restauiant,but the

英语谜语
Tom wanted to pay for his meal at the restauiant,but the waiter said ,"No,you don't have to do that.Today is my publican's birthday,so all food you had is on the house."What doea "on the house"mean here?You may answer it in Englisn or Chiness.