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.
what other waveforms are used for alternating current besides sine waves
In certain applications of alternating current, like guitar amplifiers, different waveforms are used, such as triangular or square waves.

Question: can other signals be alternating current
Self-contained rewrite: can other signals besides electrical be alternating current