Definitions for "Outer join"
Keywords:  unmatched, join, row, null, preserves
A join in which both matching and nonmatching rows are returned. The values of all columns from the unmatched table in nonmatching rows are set to NULL.
a join that preserves information from one or more of the participating documents, including elements that have no matching element in the other documents
a join that preserves information from one or more of the participating tables, including those rows that have no matching row in the joined table
Keywords:  child, parent, even, construct, showing
a relational construct that can be used to present combined data from parent and child data objects, showing all parent records even if child records for that parent do not exist