I think that defining these terms gives a lot of folks headaches.  It is one of those things that you can "know" but have a difficult time defining.  A bird who is stunning in almost every way, but has one DQ may make a good breeder bird, but you would have to realize that some portion of its offspring would inherit that one bad quality.  A so-so bird with no "bad" qualities, but also no "great" qualities probably ought to be considered pet quality, not show quality, although depending on the particular birds competing in a show, it might place well.
With males, a taller bird is generally more successful in breeding than the typier, shorter male.
Pet quality is usually used to mean a bird that doesn't make the grade for show or breeding.  It doesn;t really say that it is a bird that makes a good pet, although in general silkies make good pets.  Some birds (even some silkies), however,  have a nasty, mean or aggressive temperament, and do not make good pets.