Master Scuba Diver is not a course, but rather an experienced diver's rating. You are awarded the Master Scuba Diver rating upon completion of the prerequisites.
This certification denotes that you've reached the highest recreational diver level in the PADI System of diver education. PADI Master Scuba Diver indicates you have a significant amount of training and experience in a variety of dive environments.
The PADI Master Scuba Diver certification is the highest recreational level in the PADI system of diver education. But, you don't have to stop there! You can continue on to become a PADI Professional. As a Master Scuba Diver you'll be well qualified to begin your training as a PADI Divemaster.