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.