The marketing materials are referring to a "covered diving accident" in order to not continually refer to the specific policy wordings and exclusions necessary to define what is and is not covered.
The details will be in the policy itself. you will need to read the definitions (I have included an excerpt below) but ALSO look at the policy details, exclusions etc (like the accident has to occur while the policy is in force, injury can't be a result of an act of war... etc....etc...
I'm not sure of your country - so this doc may not be correct for you, but the DAN America Member Benefits Handbook I find on-line may provide most of the details you need.
http://dan.org/membership/handbook.pdf
In the handbook you will find the following text:
Covered Dive means a recreational dive or diving while a scuba instructor, divemaster, underwater photographer, or while performing research under the auspices and following the diving safety guidelines of the American Academy of Underwater Scientists (AAUS). A dive begins upon entry into the water and ends upon exit from the water. A Covered Dive must begin while Insurance is in force.
Covered Diving Accident means DCI as a result of a Covered Dive within the 130-foot (40-meter) limit. For Preferred and Master Plans only, it means DCI or any Injury as the result of a Covered Dive, regardless of the depth.
Hopefully that helps.