A dog show is a competition or display of domestic dogs.
Dog shows range from formal competitions based on the dog's appearance and characteristics, to competitive trials to determine the dog with the best skills and ability, to fun competitions where pet owners and novices are encouraged to participate.
Conformational Dog shows
These shows are a competition that serve the purpose of providing an evaluation of the suitability of animals for breeding. There is a minimum age for puppies, usually they must be at least 6 months old to be entered. De-sexed animals are not eligible, nor are individual dogs that have features specified as disqualifications for the breed.
Some people use the term "bench show" interchangeably with "conformation show", but technically this is not correct. At a benched show, animals are assigned to specific areas, or "benches", and they and their handlers are required to remain in or near the benching area for the duration of the show. So all benched shows are conformational, but not all conformational shows are "benched".
Bench shows began to decline in popularity in the mid-20th Century, probably due to space limitations for the animals, and ever-increasing demands on handlers' time in a changing society.  Today, these types of shows are rare. A well-known example of a benched show is the championship dog show at the Sydney Royal Easter Show run by the Royal Agricultural Society.
The "all-breed" name is a misnomer, because as of 2010, no single club in the world caters for all of the world's identified dog breeds. These shows offer competitions for the breeds and varieties of dogs recognized by the governing kennel club. All-breed shows are the strictest and most formal type of competition and are the type often shown on television.
These are events run by a breed club which may or may not be affiliated with a large kennel club. These shows are restricted to dogs of a specific breed or to varieties of one breed. For example, the Bulldog Club of America Specialty is for Bulldogs only, but the Poodle Club of America's specialty show includes the three varieties of the Poodle - Standard, Miniature and Toy.
Specialty shows may have a range of classes, from conformation to novelty, they may vary in the degree of formality, and may be run in conjunction with other clubs.
are limited to dogs belonging to one of the designated groups. For example, the Potomac Hound Group show features only breeds belonging to the Hound group. 
Other dog shows
Judging at a dog show
Impartiality is probably the most important and valued criterion for a dog show judge. The judge must put aside her personal preferences, like or dislike of the dogs' owners and handlers, any knowledge she has of a dog's previous wins or losses, and simply judge the dog before her objectively, based on its appearance and/or performance compared with the other dogs on the given day.
Handling at a dog show
A dog handler's skills are paramount and can be the difference between a winning entry or not, particularly when the competition is fierce. This is why some people, particularly in conformational shows, choose to hire professional handlers.
A handler must be able to present the dog in its best light. This may include knowing how to stack the dog and make sure it appears to best advantage, as in conformation, or giving clear, unambiguous signals to a dog in other forms of competition. Obviously, it is not to the dog's advantage to have a handler who does not understand how coat, tail, flews and feathers should be displayed, or one is not completely expert in the rules of trialling.
- The Concise Encyclopedia of the Dog.
- from AKC website. http://www.akc.org/events/conformation/beginners.cfm