There isn't necessarily a clear cut answer because everyone responds differently. You might do well with a full body workout 3 times a week, 2 sets of each exercise. If you're not looking to build, 10-12 reps may be effective. However, depending on your body type, this may not be the best workout.
Losing fat is a huge part of bringing out that definition. Getting a defined look is really more about buidling muscle and losing the fat that is covering them than it is about doing a certain type of workout.