There are many meanings and explanations of terms for AC / DC, but it is simply the type of current AC or DC!
Even if there is a rock band with the name AC / CD ! in AC, the most common AC waveform in most circuits is a sine wave. Different waveforms are used in certain applications, such as triangular or rectangular waves. It is also with audio that radio radio signals that are transmitted over electrical lines are also examples of alternating current.