Have you ever listened to a song and thought, "love the music, hate the singing". In this situation, you can use a software audio tool that specializes in trying to filter out the frequencies of the human voice. Vocal removal can be a time consuming process that involves experimentation with various audio sources, but satisfactory results are achievable. The biggest stumbling block with voice removal is the nature of the music source. If you have a highly compressed song for example that has low quality audio data, then the chances of removing the vocals are poor. On the other hand, if you are working on a high quality audio file that has a good stereo image with vocals that are center-panned, then your chances of vocal removal are much higher. Overall, it really depends on how the song has been mixed and the frequencies involved.
There's a lot of fun to be had experimenting with the songs in your music library, and with an investment in time (and a little luck), you can produce some great results. For more information on removing vocals from songs, why not read our guide on Free Software for Removing Vocals.