Ownership, in the legal sense, related to “rights” over content. (Or Intellectual Property, in this case.) Photos, Images, Drawings, Music, anything you type into a web browser and submit.
Ownership is the state or fact of exclusive rights and control over property, which may be an object, land/real estate, intellectual property (arguably) or some other kind of property. It is embodied in an ownership right also referred to as title.
Now, of the “few” public Facebook statements made they claim:
“We are not claiming and have never claimed ownership of material that users upload.”
Very much true. However, given the above two statements, their terms of service in fact strip you of your own ownership rights. See that “exclusive rights” thing there? (Emphasis added above.)
Because Facebook asserts universal rights to your “User Content”, you no longer have “exclusive rights” to it.
Once anything is posted to Facebook, you no longer own it. In perpetuity.
Or until they change their terms of service again.
I am not a lawyer, but if you are a commercial photographer, a band, a videographer, or any sort of digital media professional, don’t post anything you care about losing ownership to on Facebook.
Update: Great legal opinion about changing the Terms of Service behind your back.