I don't know anything about sailing terms, but I do understand how mechanical advantage works, and rogerstg is dead wrong about calling a truckers hitch a theoretical 2:1. If there was no friction it would be a 3:1 pulley system.

I think his sailing experience is confusing him, because I looked at the gun tackle picture, and it seems like it is used for hoisting something (a gun maybe?) into the air.

So in the interest of brevity, I present you with my masterpiece:


If you look closely, both diagrams have identical setups. The difference is which end of the rope is the load end. A truckers hitch is usually cinching something down towards a fixed object, so the top is the load end.