DSF is a new file format which allows weight-mapping info, multiple UVsets, etc. in DAZ Studio 4.  It can be used to save scenes or presets which include weight-mapped items, but can't be read in Daz Studio 3 -- if you want a preset to work in DS3 also, you need to save as .dsa

 

Tri-Ax is the weight-mapping system DAZ 3D developed -- it's called Tri-Ax because the weight-map data uses 3 axes, as opposed to 1 axis in most weight-mapping systems.