In the steady state heat conduction through a solid rod the theoretical
derivation tells that

heat in-heat out-heat accumulated =0.

What is a practical steady state heat conduction problem? what is
transient heat conduction
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 Steady state means that nothing changes with time. In your case, it means that the temperature is constant in all points of the rod. Let's begin an experiment. Say, you put a hot body in contact with a rod extremity. This extremity begins to heat, but nothing happens at the other extremity. You must wait some time (theoretically infinite in this case) for all the points in the rod to attain their equilibrium temperature. This is the transient state. Practical steady state means that the temperatures of all points are so near their final temperatures, that you can assume that the temperatures are the equilibrium ones. It depends, of course, on the precision you want to attain.