Increasingly, I have been teaching to an international audience. One of the things I find interesting about this is how the understanding of what memoir is varies dramatically from culture to culture.
Even within the culture which I am the most familiar (white, middle class American), "memoir" often evokes images of what actually is autobiography: tell-alls by famous folks. Whole life stories are usually reserved for the rich, famous, and accomplished amongst us. But those are not the same as memoir.
Memoir takes a particular period or aspect of anyone's life - known or unknown - and explores it. Memoir, versus autobiography, is more a practice of language, lyricism and expression, than a rote dictation of fact and timeline.