Denim is a more corse, industrial type fabric. Jeans have crescent front pockets and patch pockets on the back, top stitching, rivets etc., all this is more casual and jeans are built for rugged wear. I have known people who only wore jeans to work in or to ride horses.
Chinos are made from higher quality twill cotton, usually have side or quarter top pockets, piped back pockets. and are pressed and finished with a crease. Chinos can take cuffs where jeans don't take cuffs, making the chinos look more conventional. Chinos are cut more closely to a traditional office pant style, jeans are cut and fit in a more casual style.. Totally different animals.