The phrase "certified divers" refers to people who have completed a training program and received a special qualification that allows them to go diving underwater safely. Full definition
The resort even includes diving for certified divers who enjoy up to two tanks daily free of charge. (theworldsgreatestvacations.com)
A scuba review is designed for certified divers who want to refresh their dive skills and theory before heading out into open water again. (bigfishdiving.com)
Some might call the island a scuba factory, but my feeling is that it offers travelers a chance to become certified divers without breaking the bank. (globestompers.com)