Thank you, it drives me nuts how many Americans think "sushi" = "raw fish". It isn't.
Sushi, like Jauronimo said, is literally "vinegared rice".
It is *often* topped with raw fish, but like Saxum said, there are many, many other things that are also used. In addition to the ones mentioned already there's cooked fish, cooked beef, raw beef, horsemeat, whale meat, cooked eels (freshwater and saltwater), tamagoyaki (kind of omelette), squid, scallops, oysters, crab, shrimp, sea urchin, pickled cucumbers, etc. etc....
And in my experience it's not eaten all that often in Japan. Mostly just a treat for special occasions.
One of the main reasons you want to go to a "higher-end" place rather than a gas station for sushi, is that the former will have sushi chefs that are trained to identify signs of possible parasites in the raw varieties of toppings, and discard those. Been eating sushi for >40 years and never once had any health issues.