$parallaxmap
$parallaxmap
is a material shader parameter available in all Source games. It specifies the VTF texture to use for the 'sub-vertex modeling' or parallaxmap of the material surface. The texture used for this parameter is a Heightmap.
Warning:Parallax maps are disabled in every Valve game, although since an (unfinished) shader exists named ParallaxTest, which can be used as an alternative.
VMT Syntax
"$parallaxmap" <texture path> "$parallaxmapscale" <float> // Scales the $parallaxmap Y value by this amount