三輔

Etymology
三 (three) + 輔 (auxiliary; to assist: i.e. to assist in defending the capital)
 * This term was originally coined to describe three official civil posts. Each of the three civil posts also defined a specific geographic area outside of the capital at Chang'an. The three posts were:
 * 京兆尹 jīngzhàoyǐn (on the eastern outskirts of Chang'an)
 * 左馮翊 zuǒ píngyì (on the northwestern outskirts of Chang'an)
 * 右扶風 yòu fúfēng (on the western outskirts of Chang'an)

Noun

 * 1)  the three auxiliary defensive zones (which surrounded the ancient capital at Chang'an)
 * 2)  the area in and around Chang'an