buy a round

buy a/the round (of drinks)

To buy drinks, especially alcoholic ones, for each person in a group. "Next" is commonly used before "the round." If your new friend is buying us a round of drinks, then I like him already! OK, who's buying the next round?
See also: buy, round
Farlex Dictionary of Idioms.

buy a round (of drinks)

 and buy the next round (of drinks)
to buy a drink for each person present, with the expectation that one or more of those persons will later do likewise. Which one of you guys is going to buy the next round?
See also: buy, round
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • buy a/the round (of drinks)
  • a round for the house
  • round about
  • in round numbers
  • round out
  • driving
  • send round
  • argue round and round
  • tear round
  • round the twist