noun

• Φ, the 21st letter of the Euclidean and modern Greek alphabet, usually romanized as "ph".
• (mathematics) The golden ratio.
• A visual illusion whereby a sequential pattern of lights produces a false sense of motion.
• (sports) Abbreviation of Philadelphia. [The largest city in Pennsylvania, United States, and the county seat of coterminous Philadelphia County; former capital of the United States.]
• (medicine, law) Initialism of protected health information.