OK, while most people think of RAID as just for disks its really mean to describe anything. But lets talk about disks for a minute.
Different RAID levels refer to different styles of building an array. The numbers kind of imply one building on another (i.e. Raid 5 is better than Raid 4), but don't think of them as perfectly building on another.
http://rickalm.blogspot.com/2008/02/raid-and-raid-what-is-raid.html
http://en.wikipedia.org/wiki/RAID
