A rice rocket is generally a FWD econobox car, which is modded with the intent of looking like a race car, but not being one. It's a broad definition and any car can fall into it.
Ricey mods generally include vinyl, car part manufacturer stickers, with obviously no such parts found on car (ex: toyo tires decal while the car is wearing 4 mismatched no-name tires).
In essence, they are race-inspired modifications: spoilers, painted calipers/caliper covers, body kits, fake hood scoops, huge loud exhausts, etc. Also lighting: HID drop-ins into halogen housings, blue-tinted headlights or blue-ish bulbs, altezza-like tail lights (clear tail lights), clear aftermarket corners and also cheap aftermarket projector headlights.
There are more, but you get the gist.