Production: The total of all fees charged for your work.
Collection: The amount of money that actually comes in from the work you do. Unfortunately, there will always be people who don't pay their bills and adjustments to be made for insurance. Ideally, production should equal collection but in the real world few people collect 100% of their production.
Overhead: The cost of providing dentistry for your patients. This usually inlcudes everything but your own labor. That means the mortgage or lease on your building, utilities, equipment, staff salaries, insurance, supplies, payroll taxes for employees, business taxes, licenses, etc...
The typical overhead for a dentist is around 65% which means he takes home 35% of his collections before taxes. Obviously there will be a wide range of overhead percentage depending on where and how you practice - anywhere from 50% - 85%.