What does it mean to call a girl a knockout?

[Anonymous]

A guy on a dating app told me "you are what people in your country call a knockout". He's American I'm British. What does this mean?

[Josh4206]

Sounds like basically "you're the best girl" there's a word i want to use but I'm forgetting it.

[pokenstroke]

You are fucking super hot

[Luckycharms12]

You are sexy