• 祭まつり — festival
• 祭まつる — to worship; to enshrine
• 文化祭ぶんかさい — school culture festival
• 学園祭がくえんさい — school festival
• 大祭たいさい — grand festival
• 祭礼さいれい — ritual; religious ceremony
• 祭典さいてん — festival event

The kanji 祭 combines 示 (“altar”) and 肉 (rendered as 月 here) with 又 (“hand”), suggesting an offering at an altar. It originally depicted presenting meat to the gods; today it also refers broadly to festive events and celebrations.

夏なつの祭りまつりは 楽たのしいです。
The summer festival is fun.

彼かれは 神かみを祭まつっています。
He is worshipping the gods.