Thanks, John! I've found that Wikipedia is sometimes a little sparse, and the nLab is not exactly written with the novice in mind. Certainly talking to people is the way to go for a lot of these things, but I don't want to waste anyone's time! On that note, and related to your clarifying remark about corelations, do you happen to know of any terms that I should take note of when considering two partitions on the same set (rather than what I'm understanding as one partition on two sets)?