I heard a writer talking about pantsing a story. What does that mean?
"Pantsing" refers to simply writing a story without much, if any, preparation or pre-writing -- just writing down whatever comes to you, and letting the story go (and wander) wherever it feels like at the moment you're writing it down.
As for etymology, I'm not sure where it comes from. In general, "pantsing" refers to a prank in which you pull someone's pants down, but I'm not sure how that plays into the idea of writing (aside from the fact that both can be surprising).