Occlusion culling: Objects that are not in direct line of site in the players field of view aren't rendered. You'll only really notice this when it's done poorly, for example in some recent games on consoles when you turn a corner, for the briefest moment you'll see the models and textures pop in. Bungie using Umbra 3 means they'll be able to build more detailed worlds without sacrificing frame rate or increasing hardware taxation.

Ha. Thanks for the change? Not sure what else to say. I am excited to hear that Bungie is working with cutting edge tools. But if I'm being honest I really have no idea what much of that article actually means for game development.