iPhone: About standby and usage time

You can view your iPhone usage statistics by choosing Settings > General > Usage. Under the "Time since last full charge" heading you'll see two items:

• Usage: Amount of time iPhone has been awake and in use since the last full charge. The phone is awake when you’re on a call, using email, listening to music, browsing the web, or sending and receiving text messages, or during certain background tasks such as auto-checking email.
• Standby: Amount of time iPhone has been powered on since its last full charge, including the time the phone has been asleep.

Visit this page to learn more about optimizing battery life.