We say 'pasture fed' to distinguish our lamb and hogget from grass fed meat finished with grain. Grass fed is one of those terms regularly abused, like free range, and might mean that the animal was fed at some point on grass.
Our sheep spend their lives outdoors, eating grass in the fields during spring, summer and autumn with additional hay and grass pellets in winter.
Pasture fed meat can improve our health based on its higher nutrient quality, higher omega-3 content and greater omega-3 to omega-6 ratios. Red meat is high in the vitamins B12, B3, and B6, and is rich in highly bioavailable forms of iron, zinc, selenium, sodium, phosphorus, and potassium. Follow the link to this article to discover more. It refers to grass fed, but it explains how wholly grass fed meat is beneficial for human health as part of a balanced diet.
Sheep finish (are big enough) for the butcher more slowly on grass. That said that additional time spent outdoors offers an eating quality way better than grain (often indoor) fattened livestock.