for those who don't really know what it is or don't have the time to klick the link:
"What is Steam Greenlight?
Steam Greenlight is a new system that enlists the community's help in picking some of the next games to be released on Steam. Developers post information, screenshots, and videos for their game and seek a critical mass of community support in order to get selected for distribution. Steam Greenlight also helps developers get feedback from potential customers and start creating an active community around their game as early in the development process as they like."