That term started being used within the last two years or so.....it refers to the corals that tend to be "smoothed skinned" Echinata, Turaki, etc.....
If your interested in such things, start frequenting the SPS id subforum, read this:
http://www.reefcentral.com/forums/showthread.php?s=&threadid=366161
in which a number of other reference materials are mentioned. Its a great "hobby within a hobby" to get into.
Personally, I don't care for the term myself.....