You own the medium that the music was delivered on: you are licensed to play the music. In theory, the licensor (eg., Egotistic Megalomaniac Idiots) can withdraw your license, meaning you can hand the medium back and be entitled to a part refund of your original purchase price.

What the exact conditions of the license are and what they entitle you to while you are licensed depends on local law. However, I doubt you will ever see a printed listing of your entitlements, ever. I may be wrong here, but I reckon the prevailing law would be the Millenium act in the US, wouldn't it? I wonder what the equivalent would be in Europe?