Public Spaces are areas and resources on public websites that the server owner decides to open up to the public - just like a park or library (IRL).
For instance, if twitter.com
decided to open up a Public Space, they would designate https://twitter.com/.public-spaces/
to be the root of the Public Spaces API.
Public Spaces are federated APIs that can communicate with any other ActivityPub (server-to-server) service, such as Mastodon. They provide simple message services for direct messaging, group messaging and public forum messaging. Public Spaces can be utilised many different ways.
Public Spaces can also provide media storage, webhooks and other integrations.