Payment rails
Banking business day
A day on which settlement systems operate. Not the same thing as a weekday.
For euro payments the reference calendar is TARGET2’s: closed on Saturdays, Sundays, 1 January, Good Friday, Easter Monday, 1 May, 25 December and 26 December. A national public holiday not on that list does not interrupt euro settlement.
The distinction matters because every contractual deadline on a classic transfer is expressed in business days. "Credited the next business day" can mean four calendar days later around an Easter weekend. Instant rails ignore that calendar entirely.