temple festival; fair; fete day
A day of special connection to a particular deity, often marked by a festive fair with stalls on temple or shrine grounds. The explanatory gloss captures the religious origin, but in modern usage it commonly refers to the festive event itself.
Today is the festival day at the local shrine, and many stalls are set up.
When I was a child, I looked forward to scooping goldfish at the temple fair.
縁日 refers specifically to a temple or shrine fair day with stalls, while お祭り covers festivals more broadly, including ones without stalls.
festival vendor; stallholder at a temple fair
From 縁 (en, 'connection' or 'fate') + 日 (nichi, 'day'), referring to a day with a special connection to a deity. The term has been used since the Heian period.