also: こうかいひ
noun
release date; publication date; opening day
Refers to the date when something becomes publicly available, such as a movie, game, book, or event. Can also mean the first day a facility or service opens to the public.
新作映画の公開日は来月の金曜日です。
The release date for the new movie is Friday next month.
この美
The opening day of this museum hasn't been decided yet.
発売日 is specifically for the date a product goes on sale, while 公開日 is for when something is made publicly accessible (e.g., a movie, event, or facility).
開設日 refers to the establishment or founding date of an organization, facility, or system, often with a more formal or administrative nuance than 公開日.
Compound of 公開 (こうかい, 'public opening, release') and 日 (ひ/び, 'day'). The reading こうかいび is a standard rendaku (sequential voicing) form.