Yeah, it gets confusing. Both are complex, both have multiple applications...but maybe try this.
"Sets," resemble dictionary entries. They focus on one, "word," at a time, identifying one or two dominant meanings for that word. Further, sets tend to have names that pretty much identify that dominant meaning: blocking set, kicking set, coordination set, etc....they teach other things too (for example, coordination sets teach balance and stance work), and they have fighting applications (as does everything in kenpo, even the salutation), but there's that dominant emphasis.
"Forms," are closer to encyclopedia essays, and even to poems. I even like the way their missing names remind me to try NOT to lock everything down to one meaning, but to learn the moves and then follow up their multiple applications. This is why, I think (or at least it's a good argument) that the forms have themes and nicknames (Long 5: takedowns, and handling ground opponents; Long 6, "Flowering Hands; Short 2, "asterix" form), only.
Of course, there are those who think that sets and forms are worthless--a silly attitude, but there it is. I like the approach that, it seems, t'ai chi in its fighting styles has: slow forms are taught first, to operate in several ways as "touchstones," points of reference to which students can always return.
