In a nutshell, Reddit has raised the prices for access to its Application Programming Interface (API). To put it simply, an API allows information to be sent between a user and a website or app. In the case of Reddit, the price hikes have been so high that it has essentially killed off various third-party Reddit apps. This has resulted in a user revolt. Moderators of various subreddits shut down their communities in protest. Some moderators have decided to close up shop permanently until the controversial policy changes are reversed.