perhaps it's the word 'depression' that's missing - just to differentiate between a flat ground base (which this is not), and the roughly circular concave effect that is created when the remains of the pontil attachment is ground/polished out. Quality glass is often finished by breaking the attachment to the pontil rod, giving rise for the need to remove the scar by grinding and thus creating a 'depression'. Much C18 glass, however, had a kick in the base (substantial indent) which hid the pontil scar (which remained permanently).