Muscle definition is a function of two factors: muscle size and, percentage of bodyfat. If you want better definition you have to work on both elements. First, you reduce bodyfat simply by burning off all the excess fat you can. The way to do that is with lots of very low intensity fat-burning exercise like treadmill, LifeCycle, slow jogging, etc. The key here is to make sure the intensity really is low. Running hills with a 40-pound backpack is not pure aerobics. The higher intensity will cut into your recovery ability and your weightlifting workouts will have to be further apart. Fat loss is a matter of calories in versus calories out and your objective is just to burn a ton of calories over time, not to burn them all in one day or one week.
The second factor is increasing muscle size. And to dispel a common myth once and for all, there is no such thing as training for definition. A muscle can only do three thing related to size: it can get smaller, it can get bigger or it can stay the same size. There is no way to specifically train it to be more defined apart from making it bigger! And the way to make it bigger is to force it to engage in very high intensity overload. High intensity is defined as a great amount of work in a short unit of time. So it is better to do six reps with 300 pounds than it is to do 20 reps with 150 pounds. Yet the common gym mythology is high reps for definition. Not correct. High reps means you have to use low weights and that won't pack on new mass.
Sitting on a bench curling a dumbbell all afternoon won't burn as much fat as the treadmill or other activity that involves moving your entire body. When you pick up a weight make sure it's a very heavy one. The muscle you build doing that will help to keep the fat off because it will burn calories 24 hours a day, 7 days a week.
If you pay attention to these two principles, you'll soon have the ripped look you desire.