Beef is either grass-fed (typically left to wander around sparse rangeland, eating a mix of grasses and forbs of varying nutrition, given hay over the winter in cold places) or corn-fed (held in crowded barns or feedlot pens and stuffed full of corn as fast as possible). Or both: our ropey free-range cattle are sent to feedlots for 'finishing' on corn and may add 25% weight in a month or two. Corn is loaded with sugars and simpler carbohydrates than grass, which has lots of protein but requires four stomachs and plenty of rumination time to transform into berf.I don’t know what “corn fed” means (in my mind, it evokes pigs noisily snorting and feeding at a trough full of corn, which could be a good thing or a bad thing, depending on your perspective)
A 'corn-fed' person eats rich food and lots of it.
ETA: In the linked photo, taken at one of Greeley CO's many many feedlots, those elevated cows in the background are standing on ... mountains of their own shit. Hence the need for antibiotics.