A figurative or symbolical reference.
A reference to something supposed to be known, but not explicitly mentioned; a covert indication; indirect reference; a hint.
is the reference to well-known figures and/or other texts eg. "And thrice I heard the Cock crow thinking I knew it's meaning well." from COCK CROW by Rosemary Dobson The reference here is to the denial of Jesus after his arrest by one of his disciples.