A locked wiki or closed wiki is a public wiki where editing has been disabled for everybody except for a limited number of users belonging to some local or global usergroups (usually stewards). The content wikis are locked when the respective projects are closed. (See Closing projects policy). Non-content wikis may be locked when they are not needed anymore. Any locked wiki is still available to read.
The lock (soft lock) is done by removing 'edit', 'move', 'upload' and other edit related userrights (see InitialiseSettings.php for a full list) from the '*', 'user', 'autocomfirmed' and 'sysop' local usergroups and assigning them to the local 'steward' usergroup. So, among local users only stewards are able to edit locked wikis. Global users who have some or all removed userrights are also able to edit them. Currently only members of stewards, Interface editors and staff global groups have such an ability.