Conversation so far:
what is the frequency of a dc voltage
The frequency of a DC current is 0 Hertz.
what is the frequency of a ac voltage
Most countries use 50 Hz as the AC frequency.
what waveform is used for an alternating current
The usual waveform of alternating current in most electric power circuits is a sine wave.

Question: what other waveforms are used
Self-contained rewrite: what other waveforms are used for alternating current besides sine waves