This is a generic term for seafood on rice.
Rolls (mostly authentic)
There are many kinds: tuna, spicy tuna, catepillar, etc. No, the catepillar does not consist of larvae; it just looks like a big catepillar. The Japanese would not be so barbaric as to put real catepillars in it. Rolls usually consist of rice rolled around meat and veggies. Dried seaweed is often used to wrap the rolls. Then they're cut so you have a bunch of bite-sized pieces.
Rolls (American style)
California, Boston, and Philadelphia rolls: this may come as a shock, but these are not authentic. They sure are tasty, though.
Sashimi
Lots...of...raw...fish...good stuff if you get it from a good restaurant; very bad stuff if you get it from a bad restaurant.
Wasabi
This is the equivalent of guacamole. Put tons of it on your food. It will be mind-blowing.
Wasabi (the truth)
"You can't handle the truth!" and you probably can't handle too much Wasabi, too. It's Japanese horseradish--very spicy. There are three main uses for this: 1) put small amounts on your sushi or sashimi; 2) eat large amounts when hanging out with a bunch of the guys or gals to see who is the toughest; 3) clear your stuffed sinuses if you have a cold. You feel this more in your sinuses than on your tongue.
Tempura
This describes veggies, shrimp, or anything else for that matter which has been dipped in batter and deep fried. It's absolutely unhealthy for you, but who really cares?
Ginger
Slices of pickled ginger is often served with rolls, sushi, and sashimi. It's a bit spicy and slightly sour. I love this stuff.