The Top 25 sessions grid captures Tempdb space usage at the time the last SQL statement for the session completed. This grid is populated from sys.dm_db_file_space_usage.
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Session ID

The ID of the session generating Tempdb usage.

Total Space

The total space in Tempdb consumed by this session.

Application

The application generating Tempdb usage.

Host

The name of the Windows server hosting the SQL Server instance.

User

The SQL Server login name for this session.

Current SQL

The SQL statement last completed.

Internal Objects Space

The space consumed by internal objects in all tasks in this session.

User Objects Space

The total space used by user objects in this session.