n.a sparsely populated borough in which all or most of the land is owned by a single family
英汉双解大词典
pocket borough
1.
N（名词）
(before the Reform Act of 1832) an English borough constituency controlled by one person or family who owned the land (1832年议会改革前)被拥有土地的某个人或家族控制的英格兰议会选区 → compare rotten borough