DWaHMoV stands for 'Done With a High Magnitude of Velocity'. There are a lot of use of glitches such as ABHing, or 'Accelerated Backwards Hopping'.
This run uses the Orange Box engine instead of the Source 2004 engine, allowing a lot of potential.
This is the stuff of nightmares. Imagine Gordon Freeman running through the sky and flying right past you at 50 miles an hour, backwards. It's amazing to watch and laugh at at the same time.
Watch this thing here, or alternatively,
with commentary so you can learn more.
There's a lot of similar demos on the
SourceRuns wiki, along with how to do this stuff yourself.
Portal 2 and
CO-OP have also been done.