The whole car wax/polish situation is complicated and confusing. But a polish should contain a bit of mild abrasive which helps to remove the top layer of deposits and faded paint. A wax ought to be just that, without any abrasive. Emphasis on "should" and "ought".
i think dance has it down. I would like to add, they also have paint sealant - like that orange bottle Nu Finish. Its not wax, but more like a buff-on clear coat. It can look almost as shiny as wax and last a year easy. I like it, ive used it once but i stopped because i screwed up all of my back vynil trim- that stuff is brutal on vinyl. I ended up repainting all of the trim. I guess though, wax doesnt do vynil any help either- though its removal is pretty easy. That NuFinish stains black vinyl white, premanently as far as i saw it.
But that was awhile ago, and the other day i bought another bottle- this time im gonna be real careful about trim, even though i say that everytime