What is raid??

[chronicbucks]

i see everyone in here talking about Raid when it comes to a hardrive. What is RAID?? and What is the advantage

my sysem in a nutshell
i7 920@3.8ghz
Gigabyte UD4P
EVGA GTX 275
6 GB OF OCZ Platinum
windows 7

 

[spinny]

http://www.tomshardware.com/forum/43125-32-raid