What exactly is the relationship between Flow/Feed Rate and (Print) Speed? Newbie alert...
On my Ender-5, when I go into the "Tune" menu during a print and adjust the "Speed" value, that value will later be shown in the display next to a label saying "FR". I can also adjust that value by simply turning the knob during printing (and thus started to think of it as the "speed dial" ;) ).

As far as I was able to tell so far, the "FR" percentage value is being applied to all four stepper motor movements and thus allows me to slow down or speed up printing on-the-fly, e.g. to make up for sub-optimal speed settings chosen during slicing (after all, I'm still learning).

I only recently learned that FR is actually short for "Flow Rate" (or is it "Feed Rate"?) and that seems to imply that this is probably about more than just motor speed... Also, there seems to be no equivalent to the Speed setting in Octoprint: All I have on the Control tab are two distinct sliders for "Feedrate" and "Flowrate". Would I always have to move both to achieve the same effect?

Can anyone clarify? What implications of changing FR/Speed might I be missing?
By turning the knob in the main screen, you're adjusting "feed rate".
This is essentially a factor that all g-code speed settings are multiplied with - "speed dial" seems an appropriate name for it.

"Flow rate" is something different altogether - this is multiplied with the extrusion commands. It has the same effect as changing your extruders steps-per-mm.
You can adjust under- / overextrusion with this on the fly.