Source : Webster's Revised Unabridged Dictionary (1913)

Memoir \Mem"oir\, or pl. Memoirs \Mem"oirs\, n. [F. m['e]moire,
   m., memorandum, fr. m['e]moire, f., memory, L. memoria. See
   {Memory}.]
   1. A memorial account; a history composed from personal
      experience and memory; an account of transactions or
      events (usually written in familiar style) as they are
      remembered by the writer. See {History}, 2.

   2. A memorial of any individual; a biography; often, a
      biography written without special regard to method and
      completeness.

   3. An account of something deemed noteworthy; an essay; a
      record of investigations of any subject; the journals and
      proceedings of a society.

Source : WordNet®

memoir
     n 1: an account of the author's personal experiences
     2: an essay on a scientific or scholarly topic