What is the difference between AIS and GIS SUBSTATION ? What is the difference between the distribution stations?

Gas Insulated Switch gear(typically SF) and Air Insulated Switch Gear. Difference is Inddor and Outdoor applications.

AIS: Air Insulated Substation (Where insulation is made by air between the substation equipment).

GIS: Gas Insulated Substation (Where insulation is made by Gas/SF6 between the substation equipment).