Most people define dieting as restriction of food in an attempt to lose weight. There are many different paths to reach the same destination in dieting. However, that does not stop people from coming up with even more alternatives. You can try dieting on just cabbage soup all the way to dieting in "The Zone" and still reach the same weight loss destination.
Dieting can include low carb, low fat, high protein, fruits only, raw foods only, and any other combination of foods that result in a change in health and/or weight loss. While dieting does produce results, they are rarely long-term results without coupling the diet with exercise.
Dieting is done for a wide range of reasons, including healthier living, cultural trends, and peer pressure. Media bias toward perfect figures and even the popularity of shows like The Biggest Loser push people to drop pounds and strive for that perfect body, sometimes to their detriment if they take it too far.