Apparently Lips is the codename for a karaoke game that uses a specialized microphone with built-in lights and a limited motion detector. To go with the pair of mics that are included in the default package, the game itself will have 30 songs right out of the box and features the ability to import music from a CD or Ipod to sing along with. To help with that, the game somehow reduces the vocals of the imported songs, and includes a way to place the lyrics of the songs on-screen a la "normal" karaoke.
This is MS we're talking about here, so there is of course a healthy DLC component to the thing too. Lips is also going to have "hundreds of music videos" available for download to ensure that MS sees its fair share of continuing profits. However the likelihood of people paying for them, given the ability to import their own songs, is rather doubtful.