Definitions of formation:

• noun:   the fabrication of something in a particular shape
• noun:   creation by mental activity

  Example: "The formation of sentences"

• noun:   a particular spatial arrangement
• noun:   an arrangement of people or things acting as a unit

  Example: "A defensive formation"

• noun:   natural process that causes something to form

  Example: "The formation of gas in the intestine"

• noun:   (geology) the geological features of the earth
• noun:   the act of forming something