Part of owning something is the right to re-sell it if you want to.
It's the legal premise that allows for used book-stores and libraries. It's called the "First Sale Doctrine" and it means that once something's been purchased, the owner has the right to resell it without violating copyright. The law was recenlty upheld in a Supreme Court ruling which said that a student buying used textbooks in Thailand and reselling them in the US was doing so legally.
So, do you own the music you buy on iTunes? Apparently not -- you're 'leasing' it. A US District Judge in Manhattan has ruled that users cannot buy and sell songs they've purchased from iTuens. The ruling went in favor of Capital Records LLC, who alleged that music startup ReDigi had violated copyright.
ReDigi was founded in 2011 and allowed for users to swap digital music for a price much lower than they'd originally paid -- a user-to-user version of a used bookshop. ReDigi made it's money off a transaction fee.
The ruling, which shuts down ReDigi, essentially says this: e-Books, MP3s and all those episodes of Arrested Development you bought on iTunes aren't actually yours -- you're just leasing them.