What is the technical name for the push-on type of wheels that are found on some bicycle trailers?
As various people have noted, wheelchair hub is the correct term for these one-sided, push-button release hubs. 



It goes without saying that this type of mechanism is now being widely used in cycle trailers and recumbent trikes, but we still call them wheelchair hubs even though "real" wheelchair hubs have much shorter axles than are commonly found on trailers and recumbents (see image above).