Roe is the mass of eggs found inside a female fish. When you see orange bubbles on top of sushi, that's often salmon roe. Each tiny sphere is a fish egg, and thousands of them cluster together inside the fish.

Different types of roe taste different and come from different fish. Caviar, one of the most expensive foods in the world, is roe from sturgeon. Salmon roe has large, bright orange eggs that pop in your mouth. Tobiko, from flying fish, is smaller and often used in Japanese cuisine.

Fish produce enormous amounts of roe because most eggs never survive to become adult fish: they get eaten by predators, fail to hatch, or drift into unsafe waters. A single cod can produce millions of eggs at once. This massive quantity gives at least some eggs a chance to survive and continue the species.

You might also hear the term fish eggs, which means the same thing but sounds less formal.