As with any other phone, pressing the power button will bring up the lockscreen on the Lumia 925, and Nokia has added an option so you can simply double-tap the screen to also bring up the lockscreen. But, there is also a new option, which Nokia is calling "Peek", which brings up the "Glance" screen by waving your hand in front of the display. Currently, bringing up the Glance screen just shows a black screen with the time as well as a notification showing if your phone is in silent/vibrate mode.
There isn't much to it now, but this could easily be a good spot for some quick toggles, like silent/ring mode, airplane mode, WiFi, and Bluetooth toggles. Although, it's unclear if that is the plan for the future.