Sushi is a style of food, not exclusive to requring fish alone. Most of the time it's two main ingredients are rice wrapped up in seaweed (nori), but can also simply be a lump of sticky rice topped with anything from tuna to crab to eel. The nori wrapped sushi can also be fish free and simply have vegies or tofu instead. In America the "sushi" that is vegie we often typically call "California roll", if I am not mistaken.

It is an everyday style of food in Japan much like burgers and pizza are in America. Sushi we consider exotic here, but in Japan it is their diner food like Denny's. I've been to Japan, and in many suhi places, what they do, is make it without an order at all, but make it behind an open counter that has a track on it, which the chef plates and puts on that track which pulls the plate accross the counter on display, and you simply pick up the plate you like as it goes in front of you. 

I love sushi, and especially with wasabi.