noun
jubilee; semicentennial; 50th anniversary celebration
Refers to a celebration or ceremony marking the 50th year of an event, institution, or reign. Often used in formal or historical contexts.
今年は市制施行五十年祭が開かれる。
This year, the city's 50th anniversary celebration will be held.
五十年祭の記念式典に出席した。
I attended the commemorative ceremony for the 50th anniversary.
Compound of 五十 (fifty), 年 (year), and 祭 (festival/celebration). The reading ごじゅうねんさい follows standard on'yomi.