Definition of "Yacht"
I think a lot of people are going to think of a yacht in varying terms.
A yacht is a recreational boat (you don''t see a lot of shrimp yachts or cargo yachts) and size does count, but where? So sure, toss in a requirement for a galley, head and a berth (that''ll keep Sunfish from being ''yachts). Some say the minimum size for a ''yacht'' is 35'', but I''ve seen some Flickas below 30'' that I''d call proper yachts, so I''d keep anything out that was trailerable.
Remember, this is ONLY an opinion. If you want to call your Macgregor 26 a yacht, go ahead.