The weight refers the weight/load needed/taken to break the rod or line.
BUT if a rod states a 5kg weight, it does NOT mean the whole rod can take a 5kg load be for breaking.
GENERALLY as a rule of thumb from a flat horizontal 0* angle to around a 50* lifted angle will give you 100% of the rods power. Once you lift beyond 50* the rod will start to lose power and you could snap it a lot easier under less than the stated weight. BUT AGAIN this is a rule of thumb as some rods can bend over 360* and not snap and others like jig sticks will do 90*+ and spring back.
The Sydney Marine Man