You should avoid that area at night; it's known as a rough part of town.

rough 在这里是形容词，意思是"粗糙的、粗野的"，引申为"治安差的、危险的"。 part of town 指城市的某个特定区域或街区。 rough part of town 指城市中治安较差、犯罪率较高的危险区域。