noun (n)

• a position particularly well suited to the person who occupies it(noun.state)

  Example:
  He found his niche in the academic world.
  

  source: wordnet30
• a small concavity(noun.shape)

  Synonym:
  corner, recess, recession
  

  source: wordnet30
• an enclosure that is set back or indented(noun.artifact)

  Synonym:
  recess
  

  source: wordnet30
• (ecology) the status of an organism within its environment and community (affecting its survival as a species)(noun.state)

  Synonym:
  ecological niche
  

  source: wordnet30
• A cavity, hollow, or recess, generally within the thickness of a wall, for a statue, bust, or other erect ornament. hence, any similar position, literal or figurative.(noun)

  source: webster1913