What is curry?

We Japanese like "curry" very much. We usually enjoy it on steamed rice. It is almost our soul food. However, what we imagine on our tongue from the word "curry" is different from any other curry in other countries including India, Malaysia, Pakistan, Thai and so on. I think each curry in each country is quite different each other and they seem to have nothing in common. Wikipedia defines that curry is the English description of any of a general variety of spiced dishes. This definition is very obscure and chaotic. What do they mean by spiced dishes? There is no common spice used in all kinds of curry in the world. I don't understand why butter chicken is categorized in curry while demiglace or borscht is not. Wikipedia also says that curry's roots come from India which is known as the most chaotic country. It might be the reason why curry is so obscure. It might be that we don't need a clear definition of curry if it is delicious and we can recognize the dish as curry. The Indian curry I had for today's lunch was excellent.