Ground offset or common mode noise voltage
We use the term "Ground" for a local voltage we choose to define as 0V.  There does not even have to be any current flowing thru that connection. It is just a 0V potential reference.

Since it is a local reference, the term "ground" can be many used for different reasons.

The "Protective Earth" (PE) Ground is used for AC grid reference defined by some  low resistance path to conductive earth to a distribution transformer Neutral tap below into conductive soil and to copper plumbing below earth surface level.

"Floating ground" just means voltage is high impedance to protective earth ground.  

There can be many reasons for one local ground to differ from another.

Your example of 0.2V offset with respect to the scope's "earth grounded" measurement may be called an offset or a ground shift due to the current *resistance=voltage between the two 0V references.  

It could be 1A * 0.2 Ohms of resistance or 1uA*0.2 MOhms, as your measurement does not include resistance or shared current which is required to tell the reason for the difference.