I'm pushing my envelope here, but I'll try. Remember that we are all exposed to uses / applications of what we know, and I may just be in my realm and not looking at the overall definition.

On a o-scope, a square wave looks like |_| (negative going - flip it over for traditional view) and a triangular wave looks like /\ . This is due to wave-shaping circuits in the converter.

Getting pulsating DC by adding a diode to the circuit chops off either the upper or lower half of the sine wave, losing that as heat. The remaining portion is still a sine wave shape- but now with gaps in between the 'camel's humps'.

A full wave rectifier fills those gaps with what was chopped off in the other example, so now you would have a display looking much like DC (=) but with a bunch of bumps on the top (ripple from the tops of the sine waves). For a DC application, you could filter this off; the easiest way to start would be a big capacitor across the leads. On a car battery charger the ripple doesn't make a difference. On a stereo system, you would hear a hum - here in the US 60 Hz, and multiples therof.

Are we completely OT here yet?

Now, as far as the measurement - (opinion follows): Instantaneous voltage means nothing as long as it's within the safe limits for the device. Remember, we're looking at 60 times per second here. What the unit can produce on a continuous basis is what we generally are concerned with.

Last comparison - somebody else needs to jump in. You are buying a stereo. Do you want one that can produce 100 watts everywhere from 20 to 20,000 Hz (accepted range of human hearing) with less than 0.05 percent distortion with a given (limited) input signal, or one that can produce a gazillion watts - but only at one frequency and with a huge input signal, distortion not considered, and then for only a tenth of second before it smokes?
That's the difference between RMS and Peak (instantaneous measurement) for that application.

You're on the right track.