The APA (American Poultry Association) and ABA (American Bantam Associaton) offer books that detail the standard of perfection for each breed in the US. Many people have different definitions of show quality. Some think it has to win a show..others say as long as it is not DQ'd from a show it is show worthy.
Edited to add that there is also what some call "breeder quality", which may not do well at a show, but will do well in breeding to produce offspring with show potential. Pet quality does not meet the standard of perfection.
Jody