minor correction

Author: PiJoCoder

docs/relational-databases/errors-events/mssqlserver-19421-database-engine-error.md

@@ -28,7 +28,7 @@ helpviewer_keywords:
 
 ## Explanation
 
-Error 19421 is raised in the SQL Server error log when the lease helper on the Windows cluster side didn't signal the SQL Server lease worker withing the pre-defined lease period. Specifically, SQL Server calls [WaitForMultipleObjects()](/windows/win32/api/synchapi/nf-synchapi-waitformultipleobjects) waiting for the Lease timeout event to be set in a signaled state. If the function returns WAIT_TIMEOUT having exceeded the specified Lease interval, then error 19421 is raised.
+Error 19421 is raised in the SQL Server error log when the lease helper on the Windows cluster side didn't signal the SQL Server lease worker thread within the pre-defined lease period. Specifically, SQL Server calls [WaitForMultipleObjects()](/windows/win32/api/synchapi/nf-synchapi-waitformultipleobjects) waiting for the Lease timeout event to be set in a signaled state. If the function returns WAIT_TIMEOUT, because it has exceeded the specified Lease interval, then error 19421 is raised.
 
 A lease is a time-based communication mechanism that takes place between the SQL Server and the Windows Server Failover Cluster (WSFC) process, specifically the RHS.EXE process. The two processes communicate with each other periodically to ensure the other process is running and responding. This communication takes place using Windows [Event objects](/windows/win32/sync/event-objects) and ensures that a failover of the AG resource doesn't occur without the knowledge of the WSFC. If one of the processes doesn't respond to the lease communication based on a predefined lease period, a lease timeout occurs. For detailed information, see [Lease Mechanism](../../database-engine/availability-groups/windows/availability-group-lease-healthcheck-timeout.md). Also see [How It Works: SQL Server AlwaysOn Lease Timeout](https://techcommunity.microsoft.com/t5/sql-server-support-blog/how-it-works-sql-server-alwayson-lease-timeout/ba-p/317268)