A polish is a mild abrasive cleaner that cleans and smoothes the paint. It also removes oxidation, old wax, swirl marks and minor scratches. The result is a rejuvenated top paint layer, which is then ready for waxing. Polishing insures a uniform, high gloss shine. A cleaner is more aggressive than a polish.
Cleaners uses chemicals to remove old wax, bug remains, tar and other build-up.
Cleaners contain heavy abrasives to deep clean and remove severe oxidation and stains. Generally speaking, the best product to use on a clearcoat is a mild polish with gentle cleaners. These combination products get the most work done with the least effort. While a more abrasive product will generally polish the paint faster, an overly aggressive polishing product increases the risk of scratching. Even more abrasive than cleaners are rubbing compounds.