purpose

noun

• An objective to be reached; a target; an aim; a goal.
• A result that is desired; an intention.
• The act of intending to do something; resolution; determination.
• The subject of discourse; the point at issue.
• The reason for which something is done, or the reason it is done in a particular way.

  "The purpose of turning off the lights overnight is to save energy."

• Instance; example.