Memoir Definition

The dictionary definition of "memoir" is-

• a historical account or biography written from personal knowledge or special sources. (Google)
• a written account in which someone (such as a famous person or politician) describes a past experience (Merriam Webster)

To elaborate, a memoir is an account of collected memories both public or private that took place in the subjects life. Memoir has been seen as a subcategory of biography and autobiography, however, more presently it was become its own genre entirely. Unlike a biography which retells a lifetime's amount of events, a memoir usually focuses on fragments of someone's life, touching only on some events.

http://www.merriam-webster.com/dictionary/memoir
https://en.wikipedia.org/wiki/Memoir