A
professional wrestling squash is a match in which one one
wrestler
utterly destroys the other, getting 99% percent of the offense and
not selling anything. Ergo, squashing his opponent like a bug.
Usually only jobbers will get squashed--it is their raison d'etre.
It can happen to normal wrestlers under certain circumstances, though,
like a wrestler being punished for something they did backstage or for
poor performance in previous matchces. It could also be done to build
someone up someone as a superman by having them run roughshod over everyone--that's
exactly WCW tried to accomplish with Goldberg in 1998 by having him
squash just about everyone he wrestled. It worked, for the most part.
When a wrestler gets squashed, overall, it's a pretty good sign that
the promotion doesn't have much faith in them.