Elements form a type-division of effect types in e.g. magic systems, often used for rock-paper-scissors like resistance systems, where e.g. element Fire is weak against Water, but strong against Earth. The canonical example is the ancient greek fire-earth-water-air. Another is light against dark, or good against evil, or order against chaos. Element systems are typically employed in combat, magic and damage systems. Thus, the elements serve as the subject of resistance-vulnerability mechanisms. It can however be used anywhere, e.g. in crafting systems, or in interacting with the environment.
The classic elements form the entire universe and its workings including the weather - storms, lightning, earthquakes, floods, volcanos, draughts, wind, cold and heat.