Global locks are technical measures employed against user accounts to prevent them from logging in.
Unlike a local block where users are prevented from editing a particular wiki and may have limited access (including editing their talk page or emailing users if local administrators allow them to), global locks log users out of their account and prevent them from being able to log in. Global locks are usually applied to vandalism-only accounts, spam-only accounts, compromised accounts, or highly disruptive accounts that have been spotted abusing multiple wikis. Accounts that have been globally locked can also be configured to have their usernames hidden on all logs; this is used for disruptive or inappropriate names. Additional uses include Trust and Safety actions (which may include anonymizing/hiding a username), global ban enforcement and self-requested locks.