From IFWiki

South is a direction. It is one of the four cardinal directions, and one of the eight compass directions. Its opposite direction is north.

South is associated with the bottom edge of a map; most maps are meant to be read with the north-end up. If you are facing north, then south is back behind you.

The SOUTH command

Typing SOUTH means GO SOUTH or WALK SOUTH. That is, direct the player character southward from their current location. Assuming there's an exit in that direction and nothing is blocking or hindering the character, the PC will travel south to an adjacent location.

SOUTH is such a common command that it has an abbreviation: S.

South in other languages

Dutch zuid z
English south s
Esperanto suden s
French sud s
German Süden s
Italian sud s
Spanish sur s
Swedish söder s

Code Compare

Directions like SOUTH tend to be implemented both as room properties and as objects in their own right. The SOUTH command, however, tends to be parsed or reinterpreted as a GO command acting on the south object.

Code Compare: South
ADRIFT 4:Move South to Field begin.pngLiving RoomField end.png
Inform 6:The s_to property and s_obj object
Inform 7:The south direction
TADS 3:The south link property, the southDirection object,
and the defaultSouthWall object