To ‘root’ your phone means to gain administrative rights on the file system of your phone (in linux, root is the username of the master admin). With root access, you can install and uninstall anything you want on the phone.
Most phones come with limited access regarding what you can and can’t do on it. This isn’t necessarily a bad thing, because it can keep users from accidentally breaking something they shouldn’t mess with on the phone, especially in regards to the operating system. However, many manufacturers limit your rights to things that aren’t really so mission critical, too, and rooting the phone gets around this.
If you have a few unnecessary applications (bloatware) pre-installed on your phone that you cannot uninstall, rooting will give you this ability. It will also allow you to upgrade to newer versions of Android before your phone’s manufacturer and/or cell provider make the updates available to you. Be warned, though, that rooting may void your warranty.
For more info on what rooting enables you to do with your phone, check out this question.
When you “root” your phone you are unlocking the administrative privileges of the phone which by default are locked by the manufacturer. It’s similar to “Jailbreaking” in the iphone world.
Rooting your device allows you to do things like overclock or underclock your CPU, delete those preloaded apps that your phone wont delete like Amazon MP3 or Corp Calendar, install certain apps that require root access, load custom ROMs…
The manufacturers don’t want you to have access to these options for a number of reasons including but not limited to:
- They want to control and ensure a specific user experience
- Certain carriers require that certain functions are locked out because they want you to pay for them or because they are incompatible with their network
- If you don’t know what you are doing you can “brick” (render useless) your phone or at least cause enough problems where you’ll be calling tech support demanding to know why your phone doesn’t work.
In short, it means to get administrator access to the phone. To do things that a normal (non-administrator) user of the phone cannot do.