A samara is a type of fruit

Fruit

In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...

 in which a flattened wing of fibrous, papery tissue develops from the ovary wall. A samara is a simple dry fruit and indehiscent (not opening along a seam). It is a winged achene

Achene

An achene is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate and indehiscent...

. The shape of a samara enables the wind to carry the seed farther away than regular seeds from the parent tree:

• The seed can be in the centre of the wing, as in the elm
  Elm
  Elms are deciduous and semi-deciduous trees comprising the genus Ulmus in the plant family Ulmaceae. The dozens of species are found in temperate and tropical-montane regions of North America and Eurasia, ranging southward into Indonesia. Elms are components of many kinds of natural forests...
  
  s (genus Ulmus) and the hoptree
  Hoptree
  The Hoptree or Common hoptree, Ptelea trifoliata in the Rutaceae family, is a deciduous shrub or small tree. . Also known as Wafer Ash, it is native to North America, from southern Eastern Canada, the Great Lakes region and the Northeastern U.S.; southward through the midwestern and southeastern...
  
   (Ptelea trifoliata).
• The seed can be on one side, with the wing extending to the other side, making the seed autorotate
  Autorotation
  In aviation, autorotation refers to processes in both fixed-wing and rotary-wing aircraft. The term means significantly different things in each context....
  
   as it falls, as in the maple
  Maple
  Acer is a genus of trees or shrubs commonly known as maple.Maples are variously classified in a family of their own, the Aceraceae, or together with the Hippocastanaceae included in the family Sapindaceae. Modern classifications, including the Angiosperm Phylogeny Group system, favour inclusion in...
  
  s (genus Acer) and ashes
  Ash tree
  Fraxinus is a genus flowering plants in the olive and lilac family, Oleaceae. It contains 45-65 species of usually medium to large trees, mostly deciduous though a few subtropical species are evergreen. The tree's common English name, ash, goes back to the Old English æsc, while the generic name...
  
   (genus Fraxinus).

A samara is sometimes called a key and is often referred to as a whirlybird, helicopter

Helicopter

A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...

, whirligig

Whirligig

A whirligig is an object that spins or whirls, or has at least one member that spins or whirls. Whirligigs are also known as pinwheels, buzzers, comic weathervanes, gee-haws, spinners, whirlygigs; whirlijig; whirlyjig; whirlybird; or plain whirly. Whirligigs are most commonly powered by the wind,...

, polynose, or, in the north of England, a spinning jenny

Spinning jenny

The spinning jenny is a multi-spool spinning frame. It was invented c. 1764 by James Hargreaves in Stanhill, Oswaldtwistle, Lancashire in England. The device reduced the amount of work needed to produce yarn, with a worker able to work eight or more spools at once. This grew to 120 as technology...

.