Newbie Question

[Drizzt DoUrden]

This maybe a dumb question, but what are .Par files?. Is this a new format, or is there something I have to do to make them if I want to backup a DVD for a PS2?. I've looked on the net to see how to back DVD's up and looked in this forum (most links explaining DVD backup are dead links).. I've seen and got some riping software to rip my DVD, but am I missing something by not making a par file?. This is probably a stupid question, but I haven't been able to find the answer.
Thanks