n. The act or process of forming or making; the operation of composing by the union of materials or elements, or of shaping and giving form; a putting or coming into form: as, the formation of a state or constitution; the formation of ideas or of character.n. Disposition of parts or elements; formal structure or arrangement; conformation; configuration: as, the peculiar formation of the heart; a formation of troops in columns, squares, etc.n. That which is formed; anything considered as to its form, structure, or arrangement: as, the formation consisted of a mass of incongruous materials. Specificallyn. In geology, properly, a group or assemblage of rocks, whether stratified or unstratified, having a similar origin or some common physical character.n. In the classification of rock-masses as adopted by the United States Geological Survey for cartographic purposes, the cartographic unit, or usually the ultimate rock body separately named and mapped.n. In œcol., a plant society or association. See the extract and plant formation.