I have often heard this term being used by a lot of breeders and I wondered if it meant when you `mate your bitch her season right after a litter.`
Does the KC still register the pups as it seems a bit soon to breed again, or is it fine so long as you leave her for a year after that before you breed again?

Depends where you are it can mean litter on consecutive seasons or it can refer to a bitch being mated on successive days rather than with a day left between.

One of my US friends prefers to mate visitng bitches to her studs 3 days 'back to back', but if the owner or she is travelling to and from the stud then two matings with a day between.

The kennel club will register another litter to a bitch under a year as long as the breeder does not require to be registered under the 'Breeding and Sale of Dogs Welfare Act', which you would have to be if you bred more than four litters in a 12 month period.

Most breed club codes of ethics advise that bitches are not be be bred from under a year from last litter, but if they are then veterinarly evidence would be needed and a good reason.