A day off granted by an employer or service rather than by the state.
A privilege holiday is granted by an institution to its own people: a bank's founding day, a university's commemoration, a company's shutdown. The term appears in Indian and other Commonwealth employment usage.
It is not a public holiday and does not close anything beyond the institution granting it, which is exactly why it causes surprises: a counterparty is closed and no public calendar explains why.
These are outside the scope of any jurisdiction corpus, including this one. There is no authority publishing them and no list to hold — the only reliable source is the organisation itself.
A public holiday is declared by the state and closes what it names. A privilege holiday closes one organisation.
See also public holiday · de facto holiday · observed but open
We hold this as NOT HELD — an organisational fact with no publishing authority. See what we hold.