I believe that it means that there is a lot for building a structure (home) but that there exists a 25' easement on the property that is for use of the residents in the community to access the lake. This means that there may be setback allowances from the right of way where you cannot build. A survey of the property would show you where the right of way access lies on the land. The listing agent for the property should have that information available.
Hope this helps.
Prudential Connecticut Realty