As "personal historians," Tom and I often use these terms interchangeably when blogging or teaching about the concept of writing one's life stories. But does that signify that they all mean the same thing?
Non, nein, nope. Each of the terms we use to describe life writing has a discrete meaning. (The reason, quite frankly, that we mash them all together so often is that each term has "keyword" value in a blog, and using them all helps more people find our blog posts online.)
Each of you will have your own purpose in writing about your life, and each of these forms of writing has its own benefits and challenges.
Here's the rundown:
Autobiography. In an autobiography, one writes the story of the whole of one's life, a comprehensive overview of life experiences from birth (or ancestry) to the present. An autobiography usually contains factual or historical data such as names, dates, and places, and is often, though not always, more concerned with accuracy than dramatic license. Traditionally, it has been the most common form of life storytelling. An autobiography, although comprehensive in scope, does not necessarily have to be long. Autobiography is written in the first person (told from the writer's viewpoint and using the pronoun "I").
Memoir. Also written in the first person, the author writes about his/her life in a more limited scope, with an emphasis on past events viewed through the lens of the present. A memoir could be one's reminiscences about a particular time period (childhood), challenge (coping with mental illness) or experience (hiking Mt. Everest). It can also encompass stories from a wide scope of the writer's life that connect to a single theme (being a first-generation American). Also the term "memoirs" plural -- as in, "I'm writing my memwaahs" -- is essentially an autobiography but more concerned with personal experience than historical accuracy.
Personal History is kind of a catch-all term that could mean really any kind of edited life story writing, but most people think of a personal history as being more comprehensive, such as an autobiography or "life highlights" book. Usually written in the first person, but could also be a biography.
Biography. A biography is also a comprehensive account of one's life, highly concerned with accuracy, but written in the third person (using pronouns "he, she, and it") by someone other than the subject. Many published biographies are written about noteworthy or famous persons, but this is not always the case. We have written quite a few third-person biographies for clients. Some prefer to hire a writer to pen their life story from an objective point of view, so that their life stories are not perceived as self-indulgent or boastful.
A third-person biography can also encompass several different viewpoints, including the subject's friends, family, co-workers, etc. A biography can be about a person who is deceased or too advanced in years to give a complete narrative; details and memories supplied by others can help complete the story.
(Just because someone hires a professional writer does not automatically qualify the work as a biography. People often hire "ghost-writers" to write their story in the first person, compiled from oral interviews and other research. Because it is written from the subject's viewpoint, it is still classified as autobiography.)
Other forms of life writing:
Fictionalized memoir is just like it sounds -- a memoir, written as a novel. With all the dramatic license desired, because, hey, it's fiction, and the names have been changed to protect the innocent.
A Personal Essay is like a personal op-ed piece, usually describing a contemporary personal experience and voicing one's opinions about it. Usually short, a personal essay is journalistic. Think magazine article. Also "reflective essay," which means a personal essay that also includes reminiscence of past events. I guess. Personal essays can also be compiled into a collection, which then more resembles a memoir, but without so much memory. (Getting confused yet?) Personal Narrative is also a newer term that seems to me indistinguishable from a memoir, but whatever. Also "creative personal nonfiction."
The point is, what matters is that you get your life stories out of your head and into the world. In any form, or none at all!