Definition of: Trojan horse

1. In classical legend, a large, hollow wooden horse, described in Vergil's Aeneid, filled with Greek soldiers and left at the Trojan gates: when it was brought within the walls the soldiers emerged at night and admitted the Greek army, who burned the city: also called wooden horse.
2. Mil. The infiltration of military men into a potentially hostile region for the purpose of nullifying resistance against attack: compare FIFTH COLUMN.