From the link in the post above...
Pastured Poultry:
Thousands of small farms in the US and worldwide produce what is called "pastured poultry". To these farmers, pastured poultry means chickens and other poultry raised right on top of living grasses. This is accomplished by keeping the birds in low, wide, bottomless cages called "chicken tractors" that are moved to a new spot of fresh pasture once or more often each day.
This enables the birds to eat all the varied, living grasses, other plants, insects, etc., that they can find. Since chickens also need grain, they cannot be totally grass-fed, according to several experts. In the chicken tractors are grain feeders, and watering devices. Chickens will eat up to 30% of their calories in grass (and that's a LOT of grass), if allowed access to unlimited supplies. Pasturing the poultry assures that they have these supplies of living grass at all times.
A few purists want to reserve the term "grass-fed" for animals raised exclusively, 100%, on grass and nothing else. Now, ruminants, such as cows and sheep, can be raised totally on grass, but by all accounts, poultry cannot. (Nevertheless, certain of these purists claim they are raising their private poultry stock on 100% grass.) This confusion of terms has given rise to a false rumor among city meat handlers and restauranteurs that there is no such thing as "grass-fed poultry" because chickens cannot eat grass!!
A few purists say that "pastured poultry" cannot be raised in cages, that pastured poultry means poultry that is free to roam over pasture without physical restrictions. These folks include the addition of grain-based feeds for their "pastured" birds.
But in general usage around the world, "pastured poultry" means chickens raised in chicken tractors that are moved over fresh grass very often, with grain feeders available.