http://www.unicode.org/unicode/reports/tr15/ mentions both composites and combining sequences.
But it doesn't tell us the difference. I know what a combining sequence is. If I didn't know what a composite was, I'd guess it was the same thing as a combining sequence. However, the two are meant to be different, so it can't be the same. If I am getting the Unicode terminology correct, a combining sequence is like a plain ASCII letter A, with the accent following.
