
Hi,
Basically an Open Show is open to any KC registered dog. They are certainly considered 'serious' in many ways (BIS and BPIS qualify for Crufts) but they are less formal than a Championship Show. They are the usual starting point for puppies to get them used to the showing scene without exhausting them. There are also many adult dogs shown there too, and they are also a training ground for judges. But you certainly need to know what you're doing - you will need to have trained your dog in ringcraft beforehand.
:)