Please see the second to last paragraph of this article The bigger problem here is that the term DC has been overloaded For example DC orginated as an abreviation for direct current a current that does not periodically reverse direction Thus a phrase like DC voltage becomes direct current voltage which doesn t make much sense at all Further a DC current becomes direct current current which is redundant We EEs commonly refer to the DC component of a signal thereby equating the term DC to the time average of a time varying signal or if we are in the frequency domain the 0 Hz component of the signal Additionally we talk of DC voltage or current sources when we mean constant voltage or current sources Finally we refer to DC circuits when we mean a circuit without memory the voltages and currents in the circuit do not depend on past or future values of voltages and currents There are probably other examples where the term DC has become shorthand for something other than a uni directional current