This is another one of those dishes that seem to go by various names - Ceviche, Seviche and Cebiche, but whatever you call it the principles remain the same. Raw fish is "cooked" in a marinade made from some type of citrus juice, be it lemon, lime or oranges.
A while back I made a close relative of this dish called escabèche - here fish is briefly cooked before being left overnight marinating in a citrus based concoction.
The beauty of both these types of dishes is that they are a good way to get those family members that are a bit leery of eating raw fish to at least try something a bit different. You never know, you might actually get them eating sashimi before too long.