A flipper is a flat, paddle-like limb that helps animals swim through water. Dolphins, seals, sea turtles, and penguins all have flippers instead of legs or arms. These flippers work like underwater oars, pushing against the water to propel the animal forward. If you've ever tried swimming with swim fins on your feet, you've experienced how flippers work: they give you more surface area to push water, making each kick more powerful.

Flipper shapes vary depending on how the animal swims. Sea turtles have long, wing-like flippers perfect for gliding through ocean currents. Seals have shorter, stubbier flippers that help them maneuver quickly. Penguins use their flippers almost like wings, “flying” underwater while chasing fish.

The word can also mean the rubber fins that scuba divers and snorkelers wear on their feet, or even the parts on a pinball machine that you control to hit the ball. But when you hear about flippers in nature documentaries or ocean books, they're talking about those remarkable swimming limbs that help animals move through the water with speed and grace.