java - what is Gang of Four design pattern

I have recently come to know that there is a design pattern in Java called Gang of Four (GoF). I'm not able to understand what it is and what's its use. Can anybody make me clear on this? Thanks in advance.

Answer

The authors of the DesignPatternsBook came to be known as the "Gang of Four." The name of the book ("Design Patterns: Elements of Reusable Object-Oriented Software") is too long for e-mail, so "book by the gang of four" became a shorthand name for it.

After all, it isn't the ONLY book on patterns. That got shortened to "GOF book", which is pretty cryptic the first time you hear it.

Source: http://c2.com/cgi/wiki?GangOfFour