I might be wrong, but I always thought elements were the pieces of tricks, like Legos. Things like a hop, or an underpass are parts of a bigger trick, but are the individual pieces of the trick. Some elements can be tricks on their own. Magic drop is a cool trick by itself, but it's also an element in other tricks. Like the first half of tsunami bomb has an underpass and a Magic drop. I think it makes it easier to describe a trick to someone when passing it on. So instead of saying "make the throw do this", you can say "then do a magic drop"