A fletching is the term used for one of the feathers of vanes on an arrow, also a verb for the process of applying said fletchings to an arrow. For a tradtional arrow various types of feather are used, for modern day arrows (made of aluminium and/or carbon fibre) plastic fletchings are used. One of the latest developments has been 'spin-wings' where the plastic is curled over as it rises from the arrow. This increases the spin the arrow has in flight helping it's stability and therefore accuracy.
Commonly three fletchings are applied, at a slight (couple of degrees) angle, to give the arrow spin in flight, using a jig to put them on the arrow as acurately as possible.