Trailer hitch are used to tow the trailers and to carry the loads. The tow weight and tongue weight limit are specified for every model.
Trailer hitch for a passenger car costs $250-$300 with installation (in the San Francisco Bay Area). Trailer hitches come in two receiver standards: 1.25" and 2". The latter are better and fit better racks; 1.25" to 2" adapters do exist. Fortunately, the standard hitch rack for Honda Odyssey is 2". There is a specified hitch load limit for every car model, usually 100lb or 200lb. It's 200lb for Honda Odyssey. The trailer hitch is attached to the car body, not to the bumper. That means that if the unloaded receiver projects backwards, and somebody hits you from behind, the car will sustain considerable damage.
See also: bike rack.