The term 'Successful Dieter' can be summed up as a person who has achieved their desired weight loss goals. A successful dieter is someone who has been able to make lifestyle changes that have resulted in them losing weight and maintaining it. The crossword solution for this term is 'LOSER', which may seem counterintuitive, but it is actually an accurate description of someone who has been able to successfully lose weight. A successful dieter is someone who has been able to make the necessary changes to their lifestyle to achieve their desired weight loss goals.