As no meat or animal fat could be used on such days, observant Catholics would instead eat fish (typically fried in oil). It is unclear when or where the term "Feast of the Seven Fishes" was popularized. The first known mention is in The Philadelphia Inquirer in 1983.
Observant Catholics avoided meat or animal fats during certain periods and substituted fish, which were typically fried in oil. The specific origin and widespread use of the term "Feast of the Seven Fishes" are not well-documented. The earliest known reference is from The Philadelphia Inquirer in 1983.