The Left Anti Semi Join operator returns each row from the first (top) input when there is no matching row in the second (bottom) input. If no join predicate exists in the Argument column, each row is a matching row.
Left Anti Semi Join is a logical operator.
Tasks
How to: Display an Actual Execution Plan
Concepts
Displaying Execution Plans by Using the Showplan SET Options (Transact-SQL)
Other Resources
Using Joins
Help and Information
Getting SQL Server 2008 Assistance