for‧ma‧tion W2
1P [uncountable]SSO the process of starting a new organization or group [= creation]
formation of
the formation of a new government
2 [uncountable] the process by which something develops into a particular thing or shape
formation of
the substances which lead to the formation of ozone
We now know a lot more about the early stages of planetary formation.
3 [countable] the way in which a group of things are arranged to form a pattern or shape:
troop formations

in formation

PM if a group of planes, ships, soldiers etc are moving in formation, they are flying, marching etc in a particular order or pattern:
a squadron of aircraft, flying in formation
5 [uncountable and countable]CF rock or cloud that is formed in a particular shape, or the shape in which it is formed
rock/cloud formation
the canyon's impressive rock formations
6 [uncountable and countable] technical society, politics etc seen as a system of practices and beliefs
social/political/cultural etc formation
Marx founded a new science: the science of the history of social formations.