Milk protein is a relatively unprocessed form of dairy protein, consisting of both whey protein and casein protein in approximately a 20/80 ratio (slight differences may occur between species and processing).
It is also the type of protein found naturally in milk products. Cheese products are highly similar but may have varying amounts of casein or whey due to processing techniques (they tend to have more caseins in proportion to how solid their state is).
It can be bought in supplemental (powdered) form, but is most researched in its food bound form.
Benefits seen on the whey and casein pages can be applied to this page if a grain of salt is taken, as doses change. A glass of milk tends to have 7-9g protein whereas a scoop of supplemental protein tends to have 20-24g protein.