Unity 5 uses a new dynamic global illumation system, aka "Englighten", which allows for real-time GI. It apparently works by precomputing a portion of the global illumination algorithm for later use. This allows for indirect light bounces in real-time, with good performance.
This is different from other solutions available, such as voxel cone tracing and the older ray tracing method in that Unity precomputes lighting information for performance, while the other systems rely on very powerful computers to do lighting in real-time. This allows this lighting to be done with good performance on everything from high-end desktops to mobile devices, further establishing Unity as the "King of Platforms".
In this demo, I am able to rotate a directional light around while the game is running, and see the light bouncing changing in real-time. Notice how the entire scene gets lighter and darker based on how much direct light is coming in. In a traditional rendering setup, the ambient light in the scene would be constant, but Enlighten provides more realistic indirect lighting. Cool, eh?
Also, as mentioned in the YouTube description for this video, the "stepping" artifacts in the video are a result of the screen capture software I was using, not from the Unity engine itself.