Maximizing brings an app from its paused background state to the foreground. It is the window transition from a thumbnail state to a full screen state.
These are the navigator events sent when an application is maximized:
The following diagram shows the events that are received when the app is maximized: 
Your code needs to handle the reception of each of the above events and properly respond to each of them. For more information regarding each of these events, see Various States and BPS Navigator Events sections.