Stocker cattle; For me stockers are cattle I bring in to a pasture to eat down the grass on a cow calf operation. Old grass does not have the protein content of fresh grass. Stockers can be cattle brought in on new grass that was planted just for the purpose of feeding stockers.
Feeder cattle; Any cattle being fed usually for the intent of slaughter.
Backgrounding. Because of specific microbes in the rumen system, cattle on grass must be transferd from grass to feed slowly as to allow the microbes for feed to develope. There is one microbe for forage and another for starches.