Confusion in AC and DC signals I have certain doubts in the fundamentals of AC and DC signals.

Most of the time, we deal with DC signals in the form of batteries, whose waveform is a constant signal with peak as 1.5v 

However, i came across some resources, that told certain other signals are DC as well. For your reference, i have enclosed the resources and the respective waveforms here.

Figure 1


Figure 2, Please ignore the "bidirectional" word on the image.



So, are these signals AC, or DC? Both the sources have mentioned that they are DC signals (well, the first one is apparently "DC Pulsating" and the second one is a "DC time-varying". This confused me, and i wanted some better clarification and knowledge on these. From what i observe,

1) Any signal that is above or below the time axis (i.e the same polarity all the time) can be called DC?

2) If i have an AC signal, say a sinusoid, and by appropriately DC shifting it above / below the time axis, can i make it a DC signal, if the above point is true?

I would seek your expertise and your insights on these images as well, and tell me why these signals are DC.

Thank you.

Reference 1: https://www.elprocus.com/variable-power-supply-digital-control/

Reference 2: https://www.youtube.com/watch?v=fXBtTI107fQ, time: 2:31
The signal in question is a rectified sine-wave. This signal has a non-zero average, i.e. a DC component. It also has AC components at f, 3f, 5f, etc. where f is the frequency of the non-rectified signal.