Splitting the backup data between multiple files.
This is actually a fairly common way to speed up a large backup. IO is one of the slowest part of the whole process so by splitting the backup into multiple files we can reduce our backup time by quite a bit. Having multiple files will also increase your restore time but you do have to make sure that all of the files are available. If you lose one file then the whole backup is useless.
This is done by listing multiple locations for the backup.
This is an interesting use of RAID as metaphor.