A holiday on the same calendar date every year — the simple case, and still not a date.
A fixed-date rule puts an observance on the same day and month every year: Christmas on 25 December, most national days, most commemorations. It is the largest single category in the corpus at 2,198 rules.
It is still a rule rather than a date, and the distinction is not pedantry. A fixed date interacts with substitution — 25 December falls on a Saturday sooner or later, and what happens then is a separate rule the fixed date knows nothing about.
So even the simplest case has two parts: where the day nominally sits, and what happens when it lands somewhere inconvenient. Systems that store the answer rather than the two rules cannot explain either.
The opposite. A fixed-date holiday is on the same calendar date each year; a moveable one is computed.
A fixed-date rule produces the nominal date. Whether that is the day anyone takes off depends on substitution.
See also moveable feast · nth weekday rule · nominal date · substitution
We hold this as rule_type: fixed_date — 2,198 rules, the largest category. See what we hold.