New in version 2.1.
The deactivate hook is fired whenever a plugin is deactivated. Most things plugins do will automatically be handled by normal deactivation, but a plugin could use this hook along with activate to manage changes it has made external to the plugin that should be enabled and disabled.
For most use cases, plugins should be using uninstall instead of this hook, or simply relying on the fact that its hooks and filters will not run when it is deactivated.
This hook has no arguments.