"腐败选区"(rotten borough 或 decayed borough)，又称为"口袋选区"(pocket borough)，是指英国国会选区之中，由于选民总数极少，所以容易被有权势或富有之人所操控利用，并在未改革前的英国众议院影响一些具有代表性的选区，造成不公平的结果。

腐败选区是指那些拥有极少选民的选区，其地区的选民数通常少得可以被逐一地贿赂。这种选区通常在繁荣兴盛时给予选举配额，但随着逐渐衰落，选民数下降，然而选举配额并没有随之更新。其中一个例子就是12世纪时兴盛的主教城市旧塞勒姆，因为附近索尔兹伯里的崛起而荒废，却继续保有国会的两个议席。这种选区通常也被贵族所埪制，他们在参议院中已有议席，又把在众议院中得到的议席给予他们的儿子、亲戚或友人以增加他们自己在国会中的影响力。

A rotten or pocket borough, more formally known as a nomination borough or proprietarial borough, was a parliamentary borough or constituency in England, Great Britain, and the United Kingdom in existence prior to the Reform Act 1832 which had a very small electorate and could be used by a patron to gain unrepresentative influence within the Unreformed House of Commons. The same terms were used for similar boroughs represented in the 18th century Parliament of Ireland.