Meaning of UNKNOWN in English
1. A code meaning information not available. 2. An unidentified target. An aircraft or ship that has not been determined to be hostile, friendly, or neutral using identification friend or foe and other techniques, but that must be tracked by air defense or naval engagement systems. 3. An identity applied to an evaluated track that has not been identified. See also assumed friend; friend; hostile; neutral; suspect.
DOD English dictionary of military terms. Английский словарь военных терминов DOD. 2012