Valve's Vice President of Marketing Doug Lombardi is giving a talk about the Steam Greenlight process later this afternoon at The Guildhall at SMU, which will be streamed live for your viewing pleasure on Twitch.
Greenlight, of course, is the pseudo-democratic system that determines what does, and what does not, make it onto Steam. Simplistically, game makers submit their games for user approval, and once one has earned enough votes, it's in; realistically, the process is much more arcane and opaque. As Valve puts it in the FAQ, "The specific number of votes doesn't matter as much as relative interest in a game compared with other games in Steam Greenlight—we need customers to help us prioritize which games they want to see made available on Steam."
If you want to watch Lombardi (hopefully) shine more light on the inner workings of the process—the Redditor who posted notice of the talk describes him as "one of the best guest lecturers we've had"—you may do so on the SMU Guildhall Twitch channel, which we've also embedded above. It begins at 12 pm PT/3 pm ET.