noun (n)

• a message (spoken or written) that is introduced or inserted(noun.communication)

  Example:
  With many insertions in the margins.
  

  Synonym:
  interpolation
  

  source: wordnet30
• the act of putting one thing into another(noun.act)

  Synonym:
  introduction, intromission
  

  source: wordnet30
• The act of inserting; as, the insertion of scions in stocks; the insertion of words or passages in writings.(noun)

  source: webster1913