There's a long spectrum of personal writing out there, and I like to think of the word "memoir" encompassing it all. A lot of what I discuss here isn't formally memoir - essays are technically not memoir, though collections like Brenda Miller's (see a list of them here) really play with that line. Technically, a memoir is a book-length project covering a particular era or theme of one's life. But one of my mindful activities is re-defining memoir.
Autobiography holds down the far left end of the spectrum of memoir-like writing. Autobiography is something book-length that famous folks write, or what used to formally be called "memoirs" - note the plural. Unless you are a former president or athlete, chances are no one is going to read your birth-to-death story. So most of the rest of us write something to the right of autobiography.
