Any dated occasion we record, whether or not anything closes.
Observance is the unit this corpus is built from. It is deliberately wider than holiday: an observance is a dated occasion a jurisdiction recognises, and whether it closes anything is a separate field rather than a condition of being recorded.
The word was chosen because every narrower one smuggles in an assumption. "Holiday" implies a day off. "Closure" implies something shut. Neither is true of the commemorations, elective days and observed-but-open days that occupy a good share of the record, and all of them affect how many people are at work.
An observance carries a rule rather than a date. The dates are computed from it, which is why the corpus can answer for years nobody has published yet.
A public holiday is an observance that closes things. Most observances in the corpus do not.
Religious observance is a category of observance, not a synonym for the word.
See also public holiday · observed but open · optional holiday · operational status
We hold this as the observances table — 3,990 rules across 241 jurisdictions. See what we hold.