UNPIVOT is the reverse of the PIVOT operation, a mechanism for transforming columns into rows.
The UNPIVOT functionality was introduced previously using the TD_UNPIVOT table operator. This feature introduces grammar to support the UNPIVOT operator in the FROM clause of the SELECT statement.
UNPIVOT invokes the TD_UNPIVOT table operator internally. You can still use TD_UNPIVOT independent of UNPIVOT.