Note: You are currently viewing documentation for Moodle 2.2. Up-to-date documentation for the latest stable version is available here: Capabilities/moodle/role:override.
allows a user to override a capability in a role in context. note that to override a capability in role A, the user doing the override has to hold a role B so that role B is permitted to override role A. This is controlled in the roles allow override settings.
This is logical because even though a teacher might have moodle/role:override, in most situations we only want him to be able to override capabilities of the student role, and not the admin role in his own course.