Changing the visibility of a board to public, private, or team
Board admin can set the board's visibility by clicking the board's current visibility setting, to the right of the board's name, and selecting a new visibility setting.
On free and Business Class team boards, admin can set the visibility to private, team-visible, or public. Enterprise team boards have an Organization Visible option.
When a board is private, only those users added as members to the board can view or edit it. Private boards which are a part of teams are visible only to added members, unless they are part of a Business Class team or Trello Enterprise—then, they are also visible to team admin and Enterprise admin.
A board must be added to a team to enable this visibility level. A team visible board will be visible and editable by members of the team by default. Team board admins can restrict members from joining and editing the team board in the board's settings.
The Organization Visible Boards option is a Trello Enterprise feature that introduces a new level of board visibility for Enterprise users. When a board is created or set as ‘Organization Visible,’ it means that anyone who is a member of the Enterprise (on any team that is owned by the Enterprise) can view the board, regardless of the team the board is in.
A public board is visible to anyone on the internet and will show up in search engines like Google. Only those users added as members to the board can edit, but any person with the link can view, even if they don't have a Trello account.
Setting a board to public allows all members of Trello to view your board and optionally vote or comment. You can turn other features (like comments and voting) on and off for public members via the 'Settings' menu.
Note: Boards within teams that subscribe to Business Class will see additional privileges for the team's admins, such as the ability to see and edit all boards in a team.