noun (n)

• the posterior part of a human (or animal) body from the neck to the end of the spine(noun.body)

  Synonym:
  back
  

  source: wordnet30
• the back of the body of a vertebrate or any analogous surface (as the upper or outer surface of an organ or appendage or part)(noun.body)

  Example:
  The dorsum of the foot.
  

  source: wordnet30
• The ridge of a hill.(noun)

  source: webster1913