A nonpublic forum is government property that is not by tradition or designation a venue for public communication. Restrictions on speech in such a forum are examined for reasonableness and viewpoint neutrality. The government has more leeway to control access and can reserve the property for a particular use, as long as the restrictions do not suppress a viewpoint on the basis of ideology.
For example: A military base, where speech can be restricted to preserve the base’s functional purpose, allowing only certain groups to hold events if they align with the base’s activities.