Pokémon of this type can fly, many of them live at high altitudes, even. Most of them are birds and insects. Their power is mostly related with aerial and wind-related attacks. Most of them have wings, but there are also some of them that just float without wings, like Rayquaza and Gyarados.
Flying has been paired with every other Pokémon type to create a species; the introduction of Fighting/Flying Hawlucha completed all possible pairings. Until Generation V no species was ever a pure Flying-type; purely Flying-typing could only be obtained in battle by Porygon, Kecleon and Arceus, which all had signature moves or abilities to do so.
They're strong against the Bug type because, in real life, birds are natural bug predators.
They're strong against the Fighting type because it's difficult to hit something that's moving in the air.
They're strong against the Grass type because, in real life, many birds eat leaves, fruits, roots, seeds or vegetables, and also because many birds live on trees. Besides, tornados and hurricanes destroy crops as well as trees.
They're weak against the Electric type because one of the biggest cause of bird death is that they get struck by lightning while flying. And because birds are mostly on the air, they don't connect with the ground, which diverts electricity.
They're weak against the Ice type because, in real life, many birds don't resist cold temperatures, and that's the reason they migrate.
They're weak against the Rock type because, in ancient times, people used to hunt birds by throwing rocks to them, making them fall to the ground.
They're immune to the Ground type because something that is flying doesn't touch the ground, therefore, they don't get affected by earthquakes and Earth shifts.
In the beta version of Pokémon Red & Green, the Flying type didn't exist. The Bird type existed instead, and it is present in the glitches Missingno and 'M.
Every Generation has a Flying-type Legendary Pokémon except Generation IV.
The most common combination of types in the Pokémon world is the Normal/Flying typing, having 26 combinations.
This type has the least amount of pure types with only one Pokémon.
Along with the Water type, the Flying type has been paired up with every type (excluding types like ??? type and Shadow type). Some of them include: