Just the number of days you let the seed grow, it is a sprout around 4 or less days w/o any actual green plant part growing, just the root and the first leaves (not true leaves) if that. If you allow the seed to actually produce a small plant (usually arournd 5-8+days) that is fodder.
Sprouts are easier, quicker and have less mold problems, fodder has more bulk and acutal "green" parts for the chickens to eat.
Both have more nutrients available then the seed. There is alot of back and forth over whether the fodder has more food value or not (then the sprout). For feed out to grazers and buns I think fodder is better, but for my chickens I do sprouts, they love them, easy for them to eat, and easy for me to grow. I tried the fodder and quickly went back to my burlap bag sprouts.