"Northwest" and "Southwest" are the Engpsh translations for "西北" and "西南" respectively.
These terms come from the cardinal direction system, in which "northwest" refers to the direction that is northwest of a given location, and "southwest" refers to the direction that is southwest of a given location.
Example sentences in Engpsh:
The wind is blowing from the northwest.
We're going to take a hike in the northwest corner of the park.
Example translations in Chinese:
风从西北吹来。
我们要去公园西北角徒步。