Uni is sea urchin roe from the female side of the organism. It is considered a delicacy to sushi lovers around the world. The best way to describe uni to western people is that it is like eating something that tastes the way a natural sea sponge smells; with the added benefit that uni also has the consistancy of cream of wheat.
Uni's taste varies with the season. Over the course of a year, its flavor can range from being slightly sweet to midly bitter.