A flipper is a typically flat limb

Limb (anatomy)

A limb is a jointed, or prehensile , appendage of the human or other animal body....

 evolved for movement through water. Various creatures have evolved flippers, for example penguin

Penguin

Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...

s (also called "wing

Wing

A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...

s"), cetaceans (e.g. dolphins and whales; usually called "fins

FINS

FINS is a network protocol used by Omron PLCs, over different physical networks like Ethernet, Controller Link, DeviceNet and RS-232C....

"), pinniped

Pinniped

Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s, and reptiles such as some varieties of turtle

Turtle

Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...

 and the now-extinct plesiosaur

Plesiosaur

Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...

s, mosasaur

Mosasaur

Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...

s, ichthyosaur

Ichthyosaur

Ichthyosaurs were giant marine reptiles that resembled fish and dolphins...

s, and metriorhynchids.

Some flippers are very efficient hydrofoils, analogous to wing

Wing

A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...

s (airfoils), used to propel and maneuver through the water with great speed and maneuverability (see Foil (fluid mechanics)

Foil (fluid mechanics)

A foil is a solid object with a shape such that when placed in a moving fluid at a suitable angle of attack the lift is substantially larger than the drag...

). Some flippers are less foiled, with the appendages still apparent, as in the webbed forefeet seen in amphibious turtles.