main festival; main day of a festival
Refers to the primary festival event or the most important day within a multi-day festival, often contrasted with 宵祭り (eve festival) or 陰祭り (alternate/smaller festival).
The main festival will be held tomorrow.
The eve festival is fun too, but the main festival is definitely the most exciting.
Standard kanji spelling for the main festival or main day of a festival.
Alternate spelling with okurigana; less common but still used.
Compound of 本 (hon, 'main') + 祭 (matsuri, 'festival'). The reading ほんまつり follows standard on'yomi for 本 and kun'yomi for 祭, a common pattern in festival terminology.