The Town Council decided to take measures in order to benefit our area, which has remained undeveloped for the last five years.

undeveloped 是由前缀 un-（表示“不、未”）和形容词 developed（已开发的）组成的复合词。developed 来自动词 develop（发展、开发），加上 -ed 变成形容词，表示“已开发的”。undeveloped 合起来表示“未开发的”。