1) A car that, for some reason, can't or shouldn't be driven but is still show worthy. For example, some cars are too old to be safe to drive cross-country so they must be trailered.
2) The most common trailer queen can be driven. The owner is ussually so tied up in the status and appearance of his car that he has forgotten the joy of driving it and now hauls it around in a trailer to avoid dirt. These are often painfully shiny with very expensive, detailed painjobs and excess chrome. The owner will wash and polish every part of the car (even the brake pads) before the car goes in the trailer and then again after he parks it at the show. Extreme trailer queens are often hauled around in trailers that are show-worthy themselves.