A dependent lookup is a lookup table that depends on another lookup table.
A typical example of a dependent lookup table is a type lookup table and a subtype lookup table. The list of values that appears in the subtype field depends on the selected value in the type field in IDD. For example, if you selected United States in a Country field, when you enter a value in a State field, IDD lists U.S. states stored in the LU_STATE dependent lookup.