a round (of drinks)

When people drink together at a bar or party, they usually drink at about the same speed. So everyone gets a new drink at the same time. You call one group of drinks for each person a "round".

It's customary for one person to pay for an entire round of drinks for everyone, and then someone else pays for the next round. When it's your turn to pay for a round, you say:

This round's on me.

This phrase appears in these lessons: