“忘怀洞”（英语：Memory hole，又译：思旧穴）是出现在英国著名作家乔治·欧威尔所创作的小说《一九八四》（Nineteen Eighty-Four）中，真理部中温斯顿·史密斯使用的一种文档销毁工具。按小说的描述，是个带门的大火炉，把文档扔进去，历史就消失了，是斯密斯这个纪录司（英文：Records Department。新语：纪司／Recdep）职员的重要工具，可以任意“改正”历史。

小说中，温斯顿·斯密斯发现了一张照片，告诉他自己的对一个历史的记忆是错误的，虽然他一直在提醒自己这是事实，但是还是把这张重要的纸片扔到了忘怀洞里。在后来被奥勃良逮捕以后，他努力告诉自己这是事实，但是最终敌不过“友爱部”的思想改造承认这是他的“幻想”。

A memory hole is any mechanism for the alteration or disappearance of inconvenient or embarrassing documents, photographs, transcripts, or other records, such as from a website or other archive, particularly as part of an attempt to give the impression that something never happened. The concept was first popularized by George Orwell's dystopian novel Nineteen Eighty-Four, where the Party's Ministry of Truth systematically re-created all potential historical documents, in effect, re-writing all of history to match the often-changing state propaganda. These changes were complete and undetectable.