A day a currency cannot settle, wherever in the world you are trading it.
A currency holiday is a day on which a currency's home payment system is closed, so the currency cannot settle regardless of where the parties are.
This is the case that surprises people. A trade between two London counterparties in Japanese yen cannot settle on a Japanese banking holiday, though London is working normally and neither party is in Japan. The currency has a calendar and it travels with the currency.
A cross-currency transaction therefore needs every leg's calendar open, which is why a trade involving three currencies can find no settlement date in a week that looks clear in every participant's own country.
A bank holiday closes banks in a jurisdiction. A currency holiday follows the currency into every market that trades it.
A market can be open and trading a currency that cannot settle that day.
See also bank holiday · settlement date · value date · trading day
We hold no settlement or clearing calendars. This entry defines the term and demonstrates nothing, because a near-miss borrowed from exchange closures would imply coverage that does not exist. See what we hold.