sub·urb (sŭb'ûrb')
n.
A usually residential area or community outlying a city.
suburbs The usually residential region around a major city; the environs.
Definitions of outskirts on the Web:
outlying areas (as of a city or town);
suburb是专指那些居住人的地方,outskirts 是整个“外圈”.
应该差不多了吧.