What does =* mean?

This:

WHERE t.column =* s.column

...is old TSQL (pre SQL Server 2005) outer join syntax, and is not an ANSI JOIN.

Reference: SQL Server 2005 Outer Join Gotcha

I believe that is old syntax indicating an outer join condition from table1 to table2

Old style:

SELECT * FROM table1, table2
WHERE table1.yr =* table2.yr -1

New style (SQL92):

SELECT * FROM table2 
LEFT OUTER JOIN table1 ON table1.yr = table2.yr - 1

This is the old style syntax for expressing joins

It means the code needs to be replaced immediately! This style join is supposed to be a right join. Unfortunately it will sometimes be interpreted as a cross join, so the results of using this join may not be correct. Also, this syntax is deprecated and cannot be used inteh next version of SQl server.

That is the ANSI SQL 1989 syntax for RIGHT OUTER JOIN, where *= would be the LEFT OUTER JOIN.

You should note also that putting the join syntax in the WHERE clause is deprecated in SQL 2008. http://scarydba.wordpress.com/2009/09/15/no-join-predicate/ <== A timely article on this.