In digital logic, a don't-care term (abbreviated DC, historically also known as redundancies, irrelevancies, optional entries, invalid combinations, vacuous combinations, forbidden combinations, unused states or logical remainders) for a function is an input-sequence (a series of bits) for which the function output does not matter. An input that is known never to occur is a can't-happen term.
A don't-care term (DC) in digital logic represents an input sequence that doesn't influence the function output. It is also known as a redundancy, irrelevance, optional entry, invalid combination, vacuous combination, forbidden combination, unused state, or logical remainder.