To "release a song" means to send the song out to the public, so that people can hear it and buy it. You can "release" songs, movies, books, and software. Another phrase with a similar meaning to "release ___" is "introduce ___". There's not a really strong difference between the two, but if you say that something was "released", it sounds like people wanted it a little more and were waiting for it. To "introduce" something sounds like more work! Also, individual people can "release" a product, but "introducing" a product feels like it takes a larger organization of people. Here are some examples of both:
Sony has hinted that they may be introducing a new tablet computer at next week's conference.
Kanye is releasing a new album in the fall.