Playlists are private by default. Flip a playlist to public and anyone with the link can listen and save it to their own library as a live reference — when you edit the playlist, their copy updates too.
Public playlists are also discoverable: once a public playlist has at least one track that's available in the catalog, it appears in the Playlists tab of the global catalog so other listeners can find it without a link. Flip it back to private and it leaves the catalog again.