Flying squirrels are species (about 50 of them) of squirrels that are capable of flying somewhat, but by actually gliding.
They are not capable of flight in the same way as birds or bats but are able to glide from one tree to another using
(i) a membrane of skin on the sides of their body,
(ii) a cartilage spur at their wrists, and
(iii) tail
The flap of skin known as a patagium is a furry, parachute-like membrane that stretches from the wrist to ankle. The cartilage spur at the wrist is like an extra long finger that is extended and used in stretching out the patagia farther away from the body and provide better balancing in air. Their tails can be flattened out and used as a rudder while gliding.
Conservationist have studied them to be able to travel the distance of a standard football pitch by just gliding and can even make 180 degree turns.