Vertical stem.
(Unless the face is rectilinear.)

I think I've seen it called a "beard".

I thought it was a beard only if it reached the baseline.

I think "beard" is for the part that projects at the baseline (if it's there). Like I would say that the /G in Optima has no beard, while Cheltenham's is quite hirsute!

I'm tempted to make up a new term (like "jaw") but otherwise I'd go with "stem".

hhp

In type, 'beard' traditionally refers to the piece of the metal face below the baseline, usually corresponding to the descender depth.

I'd probably call this a vertical stub, or simply short vertical stem.

I think in metal "beard" (also called "neck") means the slope between the face and the shoulder.
http://typophile.com/node/91336

hhp

But where is the G Spot?

Thanks guys!