"Polish" is a word that is used many different ways in the detailing world. For me a "polish" is just a gloss enhancing product, nothing more, nothing less. A "pure polish" is one that contains no cleaning ability and offers no protection. Products like Deep Crystal Polish, M07 Show Car Glaze, are all "pure polishes". As a couple of the names above imply, many people refer to this type of product as a glaze.
"paint cleaners" is the next category. It basically describes a product that is designed to remove defects from the paint via an abrasive or chemical process. Products like Meguiars Deep Crystal Paint Cleaner. A lot of other brands call their similar products "polish", which often leads to some confusion
Of course there are some products that combine polish with a paint cleaner - cleaner polishes, like the Meguiars SwirlX.
While we're at it, let's throw some different waxes at you!
Pure waxes, as we define them, are waxes that just offer protection - no cleaning, no polish like the Meguiars Deep Crystal Carnauba Wax.
Then there are waxes with cleaning ability - cleaner waxes. This would include Meguiars Cleaner Wax.
Lastly, we have some waxes that combine polish with the protection - Meguiars NXT Tech Wax 2.0 and Gold Class Carnauba Plus being the most common.
Source is Meguiars online. This is the most simplified version of what i read and understood and its the best one i have read till now.