Here is a list of definitions for the various parameters used to describe boats.
As a general rule, parameters and ratios listed on the M. B. Marsh Design site are for the boat at its fully loaded design displacement, including full tanks, full crew, and typical cargo. The one exception is the light-ship displacement figure, which is (roughly) the weight of the fully fitted out, but unloaded, boat as it leaves the construction shed.
For multihulls, most of these parameters (with the exception of waterline beam) apply to the boat as a whole. In the case of trimarans and proas, waterline beam and length are stated separately for the outriggers, and wetted surface includes as much of the boat as would be in the water in normal operating conditions.
If you'd like to read more on where these parameters come from, a good place to start is Eric Sponberg's article "The Design Ratios", which can be found at http://www.sponbergyachtdesign.com/Articles.htm .