What is the name of centre of mass speed of an aircraft?
It describes what the velocity vector of the aircraft centre of gravity is in relation to the surface of the earth. Ground speed is the 2-D projection of your speed on the ground, climb speed is the vertical component.

Both ground speed and climb speed are very useful parameters as such: ground speed to figure out when the aircraft arrives, climb speed to adjust engine settings etc for reaching cruise altitude with a minimum amount of fuel used. The 3-D vector sum of the two has little practical use, that is probably why it has no separate name as far as I know.

The integrated signal is of more use: what is the position in 3D of the centre of gravity of the aircraft relative to earth? Pretty useful for navigation.