The quantity of a biologically active substance, such as a hormone or vitamin, required to produce a specific response.生物国际单位：生物学活性物质，例如激素或维生素，产生某种特殊效应所需的量
A unit of potency for similarly active substances, based on this quantity and accepted as an international standard.国际单位：一个相似活性物质的效能单位，以此量为基础并被作为国际标准单位