Samsung's Milk Music service is a freemium-style music app that's exclusive to Samsung devices, and in many cases is pre-loaded on phones and tablets. Milk Music is a radio-style streaming service, where you choose combinations of genres to determine the kind of "station" you'll listen to. You can save your favorite stations, and adjust the content by how popular, new, or favorited the songs are.
In the free tier you're limited to six song skips per hour, have to listen to a few ads, and must stream all of the music with a network connnection. For $3.99 per month you can remove ads, get unlimited skips, download music for offline listening and get optional station DJs.
Though Milk Music pretty tightly competes with the likes of Pandora, the fact that it's limited to just Samsung phones also in turn limits its appeal. Most users will stick with the free tier, and in that capacity will enjoy the service that's likely pre-loaded on their phone.