RAID stands for (I think) Redundant Array of Independent Disks. "Striping" is RAID level 0, and what it means is that you have two or more disks set up to appear to the operating system as a single disk. Your data gets seperated into several segments, with the segments being written to different disks. For example, let's say you've got four disks in a RAID 0 configuration. A given file will be segmented like this:
A B C D A B C D A B C D A B C D
...then all the A's will get written to one disk, B's to another, C's to a third, and D's to the fourth. The big advantage of this is that you get four times the transfer rate, less overhead. The big disadvantage is that if any one of those four disks goes bad, all of your data is lost.
There are other levels of RAID, with RAID 1, RAID 5, and RAID 1+0 (or RAID 10) being the most common. Plenty o' information about 'em available on the Web.