In tennis, a "Bagel" is when a player wins a set 6-0. The term comes from how the zero in the score resembles the shape of a bagel.
Winning a bagel means the opponent didn't win a single game in that set.
When Venus BAGELED Serena The Only Bagel Set In Williams Rivalry VENUS WILLIAMS FANS – [Bagel][1]
[1]: https://www.youtube.com/watch?v=knuS2flbNZk