Jacket, refers to the copper coating of the lead. If it is semi-jacketed(SJ) the copper does not extend all the way to the apex of the bullet. If it did, it would be full metal jacket(FMJ). Nose characteristics like flat nose(FN) or round nose(RN) describe the shape of the tip. Flat nose will give you a bit better hole in a paper target, than a round nose, but not as good as a wadcutter(WC). Soft point(SP), means the jacket does not extend all the way to the tip, and the tip is solid. Hollow point(HP), means the tip of the bullet has a hole or dimple in it, to provide for expansion when it hits mass.

Usually, in the whole scheme of things, the code starts with jacket type, then bullet shape.

Hope that helps a bit.