On Canon SLR's it makes sense that "M" stands for manual mode and "P" stands for full program mode. I'm cool with that.

"Av" indicates aperture priority mode and the acronym stands for aperture value. I can live with that, but it seems like a better acronym might have been "Ap" for aperture priority, just the way the instruction manual explains it. Oh well.

Now what do you think they call Shutter Priority? SP? Or maybe to be consistent call it "Sv" for shutter value? The S could even stand for speed since that is what you are setting: how fast the shutter opens and closes.

Nope, Shutter Priority is indicated on the camera with the acronym "Tv" which stands for Time value. I guess since you are setting the length of time the shutter will be open.