typically this means that home you are looking at shares waterfront in common with other homes in the development. So for example, a house in Rome would be in a development where there is a common beachfront area that serves all the homes in that development. The deeded access means that in the deed it specifies you have the right to use that waterfront.
Of course, without knowing the specific property it is hard to say for sure. Check the deed of the property and also work with your agent. If you don't have an agent, I will be happy to help.