A tax levied on the estate of a deceased person before distribution to heirs.
The deadline for filing inheritance tax is within 10 months of the decedent's death.
相続税 is a more common term for inheritance tax; 遺産相続税 explicitly includes the notion of the estate (遺産).
Compound of 遺産 (inheritance) + 相続 (succession) + 税 (tax).