The name root is the user name or account that by default has access to all commands and files on the Android operating system. Rooting an Android device is simply the process of gaining full, privileged, or admin control of a device, thus allowing ‘root access’ or ‘superuser’ permissions.
For those familiar with Windows, consider an unrooted Android device as being logged in as a guest. As a guest you can use applications and browse files, but you cannot make changes to your system. Rooting your Android device is akin to logging on your computer as the administrator, granting you the permission to alter files and customize your device.
The rooting process itself basically exploits a security weakness on a device, and in simple terms, grants the user executable permissions that are not otherwise there with a non-rooted device. Once a device is rooted, the user has complete control of the device. This means you can overcome limitations that carriers and manufacturers put on your device, extend system functionality, install custom aftermarket distributions of Android (ROMs), and truly make the device your own.