A formal occasion of national importance, typically involving grand or splendid ceremonies attended by the head of state, leading members of the government, etc.; (also in extended use) an important or ceremonial occasion.
Origin
Late 17th century.
Definition of state occasion in US English:
state occasion
noun
A formal occasion of national importance, typically involving grand or splendid ceremonies attended by the head of state, leading members of the government, etc.; (also in extended use) an important or ceremonial occasion.