Discipline is doing things even when you don't want. Working out even though you want to stay on tumblr or when you just feel like watching tv. Not eating all 20 cookies after you've cooked them or 10 brownies at the party. Not having 10 glasses of a sugary drink, instead only having 1 or 2. Eating in moderation and exercising a good amount per week, but still giving yourself a little room for error. And definitely not going to the gym while you are sick!
Not allowing certain foods or even food groups. Trying to make your calorie intake lower. Crash dieting and not allowing yourself to have even just 1 cookie. Restriction is depriving yourself and it is very unhealthy. Also, making yourself work out even when your sick or exercising for extremely long periods of time.
Restriction and Discipline are not the same thing. Constant and consistent restrictive behaviors are or may turn into disordered eating (even if you don't realize or understand it).