The exact definition of cull is, from dictionary.com:
"1. To choose, select, pick
2. To gather the choice things or parts from
3. To collect, gather, pluck
4. Act of culling
5. Something culled, especially something picked out and set aside as inferior."
As breeders, we MUST cull rabbits from our herd if we desire to better the breed. If we want to keep producing rabbits, we must let some go. Show breeders, those that breed to show standards, sometimes produce inferior rabbits. Those inferior rabbits we will cull, or remove, from the herd.
Each breeder has a different way of culling. Some choose to kill the rabbits that don't make their "show rabbit" standards. Others, myself included, prefer to sell the rabbit as a pet.
Those that choose to terminally cull (kill), their rabbits, generally have different reasons of doing so. Some people have had a bad experience with pet owners. Others don't have a pet market and so they don't have any way to sell pets.
Personally I choose to sell my culls as pets. I can find homes for all my pets very quickly. This area of WA just has a very good pet market. More and more people are realizing how great of pets Holland Lops - and rabbits in general - can be.