Inner and Outer Tables

The terms outer table and inner table describe the placement of tables in an outer join.

In a left join, the outer table and inner table are the left and right tables respectively. The outer table and inner table are also referred to as the row-preserving and null-supplying tables, respectively.
In a right join, the outer table and inner table are the right and left tables, respectively.

For example, in the queries below, T1 is the outer table and T2 is the inner table:

T1 left join T2
T2 right join T1

Or, using Transact-SQL syntax:

T1 *= T2
T2 =* T1