A more thorough explanation:

A traditional public forum is a public place where people have traditionally gathered to express their ideas and exchange views. Examples of traditional public forums include public streets, sidewalks, and parks. The government can regulate the use of these spaces, but any regulation must be narrowly tailored to serve a significant government interest and must usually be limited to time, place, or manner restrictions.

For example, a city may require a permit for a large protest in a public park to ensure public safety and prevent damage to the park. However, the city cannot ban all protests in the park or restrict the content of the speech.

It is important to note that traditional public forums are open for expressive activity regardless of the government's intent. The government must accommodate private speakers because the objective characteristics of these properties require it.

A designated public forum is public property that has not traditionally been open for public assembly and debate but that the government has opened for use by the public as a place for expressive activity. Examples of designated public forums include public university facilities or publicly owned theaters.

The government does not have to retain the open character of a designated public forum, and the subject matter of the expression permitted in a designated public forum may be limited to accord with the character of the forum. Reasonable, content-neutral time, place, and manner restrictions are generally permissible. However, any prohibition based on the content of the expression must be narrowly drawn to effectuate a compelling state interest, as with a traditional public forum.

For example, a public university may open a designated public forum for student groups to express their views. The university can limit the use of the forum to certain hours or days and require a permit, but it cannot ban certain viewpoints or restrict the content of the speech.

If the property is not a traditional public forum and the government has not chosen to create a designated public forum, the property is either a nonpublic forum or not a forum at all.

For example, a government office building is not a public forum because it is not a place where people traditionally gather to express their ideas and exchange views. The government can restrict speech in a nonpublic forum as long as the restriction is reasonable and not based on the content of the speech.