Superwash wool is wool that can be run through the laundry (washer/dryer) without the wool shrinking. Wool shrinks when the scales lift up and rub against each other, thereby locking down on nearby fibers and "felt"; hot water and agitation (i.e washing through the washer/dryer) are the usual culprits that cause felting. As a note, the number of scales on a given strand also give a certain amount of curl.
There are two ways to get superwash wool, but either way reduces the number of "scales" ( or the cuticles) of the hair by either:
1) shaving scales off each strand, thereby reducing crimp and the potential for felting and shrinking.
2) glueing the scales down by coating it with a special polymer
Superwash wool often has a "smoother" feeling than regular wool.
Recently, a friend of mine who is a hairdresser told me how the new "Brazillian Blowout" straightens curly hair --- essentially, each hair strand is "coated" with a glue (much like superwash wool) to straighten it.
It also feels "smoother" than regular hair.
Basically, the Brazillian Blowout creates superwash hair.