what is a no clipping hack?

Actually I've seen other people post pictures of this same thing in the forums but it was a couple weeks ago...
I'm having a new computer built so I didnt wana mess with installing or reinstalling until I could get my new rig hooked up. I am honestly having other issues with the game (mostly framerate and such) but other people have said its prolly a combo of server latency and my computer...on saturday, i didnt have any problems so im assuming it's partly on their end. I just wanted to report this because it seems if enough people mention it they will acknowledge the issue. I don't have any problems falling through things or anything within any other area, which is why I assume it is a bug. This happened to me during beta phase 4 as well, where i fell through by the aetheryte but others reported it so i didnt bother.