What do the terms mean?

Coated or single-coated: one air-to-glass surface(ATGS) is coated with a single layer of antireflection material, usually MgF2
Fully Coated: All ATGS are single-coated
Multicoated: at least one ATGS surface has been coated with multiple layers, the rest are single coated or not coated.
Fully Multicoated: all ATGS are covered with multiple coatings.

Coated or single-coated: one air-to-glass surface(ATGS) is coated with a single layer of antireflection material, usually MgF2