祺 is a bound-form character meaning 'auspicious' or 'good fortune'. It's not used alone in modern Chinese — you'll find it in written blessings and formal well-wishes at the end of letters or greeting cards, often paired with 福 (fú) or 时 (shí) in expressions like 福祺 ('happiness and auspiciousness') and 时祺 ('season's greetings'). It carries a classical, polite register.