XJ's are what we are about here, some call them the small or Classic Cherokees '84 and up.
ZJ's are the Grand Cherokee's up to '98.
WJ's are Grand Cherokee's from '99 on.
MJ's are the pickup version of the XJ.
YJ is the square headlight Wrangler which was replaced by the current round headlight Wrangler.
I'm not going to explain what a BJ is, if ya have to ask....