A Remote Administration Tool (known more commonly on the Internet as a RAT) is used to remotely connect and manage a single or multiple computers with a variety of tools, such as:

* Screen/camera capture or control
* File management (download/upload/execute/etc.)
* Shell control (usually piped from command prompt)
* Computer control (power off/on/log off)
* Registry management (query/add/delete/modify)
* Other product-specific function

Many trojans and backdoors have remote administration capabilities allowing an individual to control the victim’s computer.


Source : Wikipedia