for·ma·tion / fôrˈmāshən/ • n. 1. the action of forming or process of being formed: the formation of the Great Rift Valley.2. a structure or arrangement of something: a cloud formation. ∎  a formal arrangement of aircraft in flight or troops: a battle formation | the helicopters hovered overhead in formation. ∎  Geol. an assemblage of rocks or series of strata having some common characteristic.DERIVATIVES: for·ma·tion·al / -shənl/ adj.

formation
1. (plant formation) In vegetation description and analysis, a classificatory unit which usually implies a distinctive physiognomy rather than a distinctive species composition. In detail, the various phytosociological traditions ascribe slightly different meanings and hierarchical status to the term. The early European schemes grouped associations into alliances and then formation groups (e.g. sclerophyllous scrub), and then formation classes (e.g. sclerophyllous woodland and scrub). The formation classes are roughly equivalent to the major world biomes.

2. See formation type.

3. The fundamental unit used in lithostratigraphy. Specific features distinguish one rock formation from another. The thickness of the formation is unimportant in its definition, as a given formation may vary within different outcrops. Formations may be subdivided into members and together several formations constitute a group.

formation
1. (plant formation) In vegetation description and analysis, a classificatory unit which usually implies a distinctive physiognomy rather than a distinctive species composition. In detail, the various phytosociological traditions ascribe slightly different meaning and hierarchical status to the term. The early European schemes grouped associations into alliances and then formation groups (e.g. sclerophyllous scrub), and then formation classes (e.g. sclerophyllous woodland and scrub). The formation classes are roughly equivalent to the major world biomes.

2. See FORMATION TYPE.

formation The fundamental unit used in lithostratigraphy. Specific features distinguish one rock formation from another. The thickness of the formation is unimportant in its definition, as a given formation may vary within different outcrops. Formations may be subdivided into members and together several formations constitute a group.

Formation

a formal assembly of troops; arrangement of rocks in a geological setting, 1815.

Examples: formation of clouds, 1808; of troop, 1796.