A state in which ultimate legal authority rests with the central government, which may delegate powers to regional or local bodies but can in principle revoke them.
In more detail
France and Japan are commonly cited as unitary states. Unitary does not mean centralised in practice: a unitary state can be highly decentralised. The distinction is legal, namely whether regions have constitutionally protected authority. Lijphart treats the federal–unitary contrast as one of the two main dimensions separating consensus from majoritarian democracies.