What is HijackThis?

Hello friends I want to know whta is HijackThis?
I have heard a lot about HijackThis on this forum, but i dont know what is is & how it works? Can anyone out there explain me what is HijackThis?

HijackThis is an enumerator that produces a listing of certain settings and files on a users PC. hijackthis.exe is a process belonging to Merijn Hijackthis and monitors your browsers configurations and plugins. Modifications and restores can be made when necessary. This program is a non-essential process, but should not be terminated unless suspected to be causing problems.

HijackThis will scan your systems registry, and other various system files. What it looks for is files and settings that spyware or hijacker programs would leave behind. After the program gets completely done scanning your system, it will display a report that you can view and understand.
It can also give you information that will hopefully help you to remove the infection from the files or registry entries.

Here is a guide on HijackThis!
http://forums.techarena.in/guides-tutorials/1029054.htm