final boss

/F AY1 N AH0 L B AA0 S/
noun
  1. 1

    (video games) An extremely powerful enemy that a player fights at the end of a campaign or story.

  2. 2

    (figuratively, informal) The best or ultimate example of something; an epitome.

  3. 3

    (figuratively, informal) An extremely difficult thing that one needs to finish or beat in order to complete some task.