In tennis, what is the slang term for a 6-0 set?

In tennis, a 6–0 set is called a bagel.

The nickname comes from the visual resemblance between the numeral zero and the round shape of a bagel. A player who wins a set 6–0 is said to have “served” or “given” a bagel, while the player who loses it has been “bagelled.” The term is informal, but it is widely understood in tennis reporting and commentary.

A bagel is not the same as “love,” although love is the traditional tennis word for zero in point and game scores. “Donut” and “shutout” communicate the idea, but they are not the standard English tennis slang term. A 6–1 set has its own nickname: a breadstick.

Two bagels in one match are commonly called a double bagel. A much rarer achievement is a golden set, in which a player wins every point in a set, not merely every game. Thus, a 6–0 score does not automatically mean the winner lost no individual points.