noun

1. a forming or being formed
2. a thing formed
3. the way in which something is formed or arranged; structure
4. an arrangement or positioning, as of troops, ships, airplanes in flight, football players, etc.
5. Ecol. the major unit of vegetation usually extending over a large area, as the prairie, deciduous forest, tundra, etc.
6. Geol. a rock unit distinguished from adjacent deposits by some common character, as composition, origin, type of fossil, etc.

Etymology: ME formacioun < OFr formation < L formatio < pp. of formare: see form