Yamaha terms and abbreviations for digital pianos:
weighted action - just what it says. Some kind of generic weight has been added to all keys to give a weight, though not a graded or yet a hammer-action reponse!
GHS - yamaha entry level graded hammer action
GH or GHE - mid-level graded hammer action
GH3 - new generation graded hammer action
NW - natural wood action
I have listed these from basic to best.