What category are nuts classified as?

I think nuts is a class of its own.

I know that peanuts are legumes because of the way that they grow, but I always thought nuts and seeds were in their own category. I guess they can be considered a fruit in some ways, but I don't always trust what Wikipedia says. I know that, for nutritional purposes, they are usually classified in their own category. They have different composition than a fruit, but they have some similarities, too.