forgot which book something is in.
 

I believe it's a pyramid, but I don't remember which one.

it's the rules for a large creature attacking with a sweeping motion against more than one enemy. Sort of like the "cleave" from dungeon fantasy powerups.

I just breezed through it because I was looking for something else. Unfortunately I didn't commit it to memory.

does anyone remember?

Re: forgot which book something is in.
 

I suspect you're thinking of either the rules for "Big Swings" (effectively attacking an area with a melee attack, relying on being sufficiently larger than your target that they can't easily avoid), or "Didn't See You There" (large creatures can just move through the spaces of smaller ones and incidentally trample them). Both rules are in "Combat Writ Large", in Pyramid #3/77, "Combat".

Re: forgot which book something is in.
 

(Oh man, they really put "cleave" in DF? Here I had been so proud that my favorite RPG system did not have a multi-target attack ridiculously named "cleave"... oh well.)

In The Fantasy Trip, it's called a "sweeping blow" (q.v. Advanced Melee), though that's not GURPS.

And there is Multiple Targets in Martial Arts p.127, which is a cinematic rule covering what you're talking about, but it sounds like it's not the one you meant if it's in Pyramid and is specific to slashes.