NAS stands for Network Attached Storage. That pretty much explains it. Save it in one place and access from everywhere. So it is a centralized Hard disk you say? Uh yes - sort of (but it does not sound that cool does it? ) Here is a nice video explaining it well:
Manjaro 64bit on the main box -Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz and nVidia Corporation GT200b [GeForce GTX 275] (rev a1. + Centos on the server - Arch on the laptop. "There are no stupid questions - Only stupid answers!"