What does “nHD” mean?
This either means “NhaNc3d HD” or “near HD” – probably the former. It is an abbreviation used by the non-scene release group “NhaNc3”, who operate over P2P, namely through MovieX.info. Their arguent is that their nHD releases are optimized to allow playback on lower-end processors.
Here’s an example; “Spiderman.3.2007.720p.nHD.x264.NhaNc3”.
Thanks to commenters for finding this information!