What is steady heat flow?

In most realistic situations heat flow can be said to occur from a region of higher temperature to one of lower temperature. As the region of higher temperature loses heat and the other region gains heat their temperatures become closer and the rate of heat flow diminishes.

If, however, it can be contrived to maintain the source of heat at a constant temperature and the destination of the heat also at a constant temperature, then the heat will flow between the two at a constant rate, called steady heat flow.