earthing means zero potential grounding means which 
equipment we want keep the zero potential it is connected 
to earth.

grounding:
this means keeping that particular terminal as common point.
example-1.
consider the case in electronic circuitry(as with a music 
system) where dc supply is used, the negative terminal is 
usually grounded to other metallic parts of that system.
example-2.
take any circuitry where a number of different voltages are 
used, 0-12v, 0-24v, 0-110v, 0-230v etc. here all the ov 
terminals are grounded and taken it as common.
earthing:
this means making the common point to earth.the potential 
of this point shall be Zero volt.
example-1.
transformer neutral is earthed to keep the potential as 
zero.
example-2
equipments are earthed for better safety of living beings.