What does it mean when a doctor refers to water behind the eye as macular degeneration?

Wet type. I think he means there is leakage in the macula which is the wet type of macular degeneration.
Wet AMD. There are two type of macular degeneration. The most common and less problematic is dry macular degeneration(amd). About 10% of dry amd to change to wet either blood vessel leaks to macula or bleeding. Thsi can cause vision problem. But, there is a treatment for wet amd. If there is any changes in vsiion, distortion please see an ophthalmologist asap.