"Northeast" and "Southwest" are the Engpsh equivalents of "东北" and "西南" respectively.
These terms come from the cardinal directions. In Engpsh, "north," "east," "south," and "west" are the four cardinal directions. "Northeast" and "Southwest" are formed by combining the cardinal direction "north" or "south" with the ordinal direction "east" or "west".
For example:
"The storm is heading northeast." (暴风雨朝着东北方向移动)
"The city is located in the southwest region of the country." (这个城市位于该国西南地区)