SET FMTONLY

SET FMTONLY { ON | OFF }

SET FMTONLY returns only metadata to the client. 

For 'regular' tables - the result set only have headers of the results but no data.

SET FMTONLY can be used to test the format of the response without actually running the query.

SET FMTONLY ON

GO

-- no rows will be return (only the headers):

SELECT * FROM [dbo].[StamTable2]

GO

SET FMTONLY OFF

GO

-- all the rows will be return:

SELECT * FROM [dbo].[StamTable2]

GO

http://msdn.microsoft.com/en-us/library/ms173839.aspx

http://msdn.microsoft.com/en-us/library/ms173839(v=sql.100).aspx

What is metadata?

The short definition is that it’s data about data.

Metadata is used to add context and understanding about data that users are accessing, or to hide complexity from end users who aren’t required to know or understand the technical details of data.

(from MSDN SQL Server Metadata Toolkit: http://archive.msdn.microsoft.com/SqlServerMetadata)

See an article about Using SQL Server meta data to list tables that make up views:

http://www.mssqltips.com/tip.asp?tip=1638

SQL Server Denali introduces new metadata discovery capabilities, removing the need to use the older SET FMTONLY option:
http://www.sqlmag.com/blogs/puzzled-by-t-sql/entryid/76283/denali-t-sql-at-a-glance-metadata-discovery