commemorative festival; anniversary celebration
Refers to an event or festival held to commemorate a person, historical event, or anniversary. Often used for public ceremonies, school founders' days, or memorial festivals.
Next month, a commemorative festival will be held to celebrate the 100th anniversary of the town's founding.
At the school's anniversary celebration, a lecture was given by an alumnus.
祭り is a general term for a festival, often traditional or religious, whereas 記念祭 specifically implies a commemorative purpose.
Compound of 記念 (commemoration, memory) and 祭 (festival). The exact historical derivation is uncertain, but the word follows a common Sino-Japanese pattern for naming formal commemorative events.