A: In some general contexts, memoir and autobiography can be used interchangeably. In fact, Amazon.com puts them in the same category. But there’s a key difference that publishers use to define each—the timeline covered in the writing.
(Get more advice in The Everything Grammar and Style Book)
An autobiography focuses on the chronology of the writer’s entire life while a memoir covers one specific aspect of the writer’s life. So, if I chose to write about my complete life up to this point—including growing up in Cincinnati, my time in New York, the few years I spent in Chicago and eventually landing at Writer’s Digest—I’d write an autobiography. If wrote a book about the winter of my sophomore year in high school where I got my tongue stuck to an icy pole, I’d write a memoir.