parity is a form of error checking
raid 5 is striped with parity
any data that you save will be striped across all 10 drives
parity gives the computer something to compare against in case one of the drives fails, you just swap it out with a new one, and all the data that was on it will be reconstructed

raid 5 is a VERY secure method of storing data, although pricey
a cheaper method would be to use mirroring (raid 1), where the same data is written to multiple drives, but its a reduction in space