'Conflat' is the telegraphic code within the Great Western Railway's coding of railway wagons for a container wagon. Unlike normal wagon loads, containers were only listed to carry furniture or goods (unless they were refrigerated containers, which carried frozen products kept cold by ice) which needed to be placed on a specialist flatbed wagon which had train braking capability due to the fragile nature of the products carried.
The wagons were removed from service (as were the containers themselves) when more modern containers came into use.