What does it mean "to be a certified diver"?

As a certified diver you will be able to dive with a buddy independent of supervision while applying the knowledge and skills that you learn in the course, within the limits of your training and experience. Obtain air fills, scuba equipment and other services. Plan, conduct and log open water non stop (no decompression) dives when properly equipped and when accompanied by a buddy in conditions with which they have training and/or experienced. Continue their dive training with a specialty dive (Adventure Dive) in the PADI Adventures in Diving program or in a PADI Specialty course.