If you draw the flight envelope, or V-N diagram, the points labelled around in in clockwise order are a (Va / manoeuvre speed),
Vb (rough air speed), Vc (cruise speed), Vd (design limit speed)...
(Courtesy of Wikipedia.)
That's one of the reasons we have Vfe not Vf, and don't use Vg for the gear limits - structural engioneers already use f and g for negative g structural points.
In aircraft structural engineering, the curve between the origin and the manoeuvre speed/g-limit point is called the O-A curve.
So, really it's just a labelled point around a diagram.
G