There are 7 levels of recreational diver in the PADI universe. They are listed in order of progression.
Discover Scuba Diving
This is a one-day PADI program that offers you the experience of scuba diving to 12 metres. It does not result in a certification but can be credited towards your first open water certification, be that either Scuba Diver or Open Water Diver. This is perfect for those who are interested in finding out what it is like to breathe underwater and experience what it is all about.
This is the entry level course. The scuba diving course can be completed within 2 days with some online eLearning. Once completed, you will be able to dive to a maximum depth of 12 metres with a PADI professional guide.
Open Water Diver
This is the first course whereupon you will be able to consider yourself as a diver. The duration can be completed in 3-4 days with online eLearning. Once you complete the open water diver course, you will be able to dive to a maximum depth of 18 metres with a buddy or guide in similar conditions to what you learned.
These are a variety of specialty diver courses designed for a specific diving activity i.e. digital underwater imaging, deep diver, underwater navigation, NITROX, search and recovery to name but a few. Most an be completed within 1 or 2 days.
Advanced Open Water Diver
The advanced open water diver course is a 2-day, 5 dive course. You will conduct 5 training dives on 5 individual skill sets. Two of these are compulsory. A deep dive and an underwater navigation dive. Then 3 others from a supplied list. There is some theory, but not as much as the open water course. you will need to complete the 5 Knowledge reviews of each of the 5 subject dives.
The rescue diver course is a 2-3 day course involving theory, a pool session open water training dives. This course will give you skills for self rescue, recognizing and managing stress in other divers, emergency management and equipment, rescuing panicked divers and rescuing unresponsive divers.
Divemaster Scuba Diver
The divemaster scuba diver rating places you in a very select group of divers who have the experience and scuba training. Fewer than 2% of recreational divers attain this rating. It is the top of the ladder in the PADI universe of recreational diving. To reach this level you must be a Rescue Diver and have 5 PADI Specialty Diver certifications along with a minimum of 50 logged dives.