I just read on the side of a Cranberry Juice pack that one of its ingredients was Cranberry compound? What does it mean?
I honestly cannot think of anything they'd be referring to other than a chemical compound, which, in layman's terms, is basically anything more complex than a pure element like oxygen.
A cranberry - and any other food - contains an enormous number of "compounds", so I'm pretty sure that the phrase "cranberry compound" just means that it's not made from fresh/whole cranberries. It either uses some kind of artificial flavour or concentrate.
If it says "from concentrate" then it is almost definitely the latter; if it says "no artificial flavours" and nothing else then it might be the latter, and if it says "not from concentrate" (but doesn't say anything about artificial flavours) then I'd guess it to be the former.
I'd love to post some kind of citation, but as I said, I don't think it refers to any specific thing, it sounds more like a weasel word to avoid listing one or more "chemical" names like "proanthocyanidin".
I am not 100% sure, but I believe compound is fruit (in your case cranberries), which were cooked with sugar. There are IMO certain similarities between the english compound and the german word "kompott". See also the wiktionary entry to kompott.