MR16 is multifacited reflector 16 eights of an inch diameter.
GU 10 is a type of base.
Many GU 10s are MR16s.
True, but most MR16's are 12v, and most GU10's are 230v; so maybe one tends to categorize the difference based on the voltage.
I have not seen a ELV bulb using the GU10 base.