From IFWiki

Northwest (or north-west) is a direction. It is one of the four diagonal directions, and one of the eight compass directions. Its opposite direction is southeast.

Northwest is associated with the top left corner of a map; most maps are meant to be read with the north-end up. If you are facing north, then northwest is in a diagonal direction both forward and to your left.

Some early IF games do not support diagonal directions like northwest. In ADRIFT Generator 4.00, diagonal directions are initially disabled and must be explicitly enabled by an ADRIFT author before they can be used in a game.

The NORTHWEST command

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

NORTHWEST is such a common enough command that it has an abbreviation: NW.

Northwest in other languages

Some languages and regions prefer to hyphenate the names of diagonal directions. Some language library extensions support both spellings; others don't. Only the unhyphenated variants are listed here.

Dutch noordwest nw
English northwest nw
Esperanto nordokcidenten nw, nok1
French nordouest no
German Nordwesten nw
Italian nordovest no
Spanish noroeste no
Swedish nordväst nv

1 Esperanto's words for northwest and northeast are nordokcidento and nordoriento, which means it's problematic to use no as an abbreviation for either of them. One might borrow the English abbreviation nw, but it's not ideal since there's no W in the Esperanto alphabet. There aren't enough Esperanto IF games to see any clear concensus on how to abbreviate nordokcidenten, but nw and nok seem the most likely possibilities.

Code Compare

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

Code Compare: Northwest
ADRIFT 4:Move NorthWest to Field begin.pngArmoryField end.png
Inform 6:The nw_to property and nw_obj object
Inform 7:The northwest direction
TADS 3:The northwest link property and northwestDirection object