Must-Use plugins (mu-plugins) are a specialized class of WordPress extensions that are located in the /wp-content/mu-plugins directory. Unlike standard plugins, they are automatically loaded by WordPress and cannot be deactivated through the administrative dashboard. This makes them an essential tool for enterprise-level developers who need to enforce specific site configurations, security protocols, or performance filters across a multisite network or for a high-value client who might accidentally deactivate a critical piece of site infrastructure. Since they load before standard plugins, they are also highly efficient for modifying core behaviors via early-priority hooks.
Glossary entry