Unless the lock level is MVCC or TABLE, pages are locked for reading in shared mode. A shared lock on a page does not prevent multiple users from concurrently reading that data.

However, a user trying to change data on the locked page must wait for all shared locks to be released, because changing data requires exclusive locks.

This can be a problem if one user is running a long report that accesses a table with a shared lock. No users can make changes to the locked table data until the report is complete.