Maximum lag can be used when MediaWiki is installed on a database replicated cluster. To save actions causing any more site replication lag, this parameter can make the client wait until the replication lag is less than the specified value. In case of excessive lag, error code maxlag is returned with a message like Waiting for $host: $lag seconds lagged.
See Manual: Maxlag parameter for more information.
The database is currently locked to new entries and other modifications, probably for routine database maintenance, after which it will be back to normal.
The system administrator who locked it offered this explanation: Major Server Maintenance, Access wil be restored soon.
