iOS: Understanding passcodes

You can use a passcode on your iPhone, iPad, or iPod touch to protect your information and data. Each time you turn on or wake up the device, it will prompt for the passcode before you can access applications or information on the device. This article provides resources and tips for using passcodes. For full details on passcode lock and settings, refer to the User Guide for your product.

Source: Apple - Support - Most Recent - iPhone