Nrsimha Chaturdasi is the day Lord Nrsimhadeva (nri-SING-ha-deva) appeared on the earth.
After Varahadev killed the demon Hiranyaksha, the demon’s younger brother, Hiranyakashipu, performed severe austerities which made him the most powerful being in the universe. Although Lord Brahma could not grant him immortality, he did give Hiranyakashipu blessings, that he could not be killed by any man or animal, by anything living or dead, during the day or night, inside or outside, on the land or in the sea or sky.
Although seemingly invincible, Hiranyakashipu tormented his youngest son Prahlada in many ways, but because he was a pure devotee of Lord Krishna he was not harmed. Then, the Lord burst out of a palace column as Nrisimhadeva. By killing Hiranyakashipu in the form of a half-man and half-lion, with his fingernails, at dusk, in the threshold of the palace and on his lap, Nrisimhadeva simultaneously respected the blessings given by Brahma and saved His dear devotee Prahlada Maharaja.