在考研英语中，冒号（:）通常用于 表示解释说明，即冒号后面的内容是对前面某个名词或短语的进一步解释或阐述。例如，在句子“The NT Rights of Terminally III law means he can get on with living without the haunting fear of his suffering: a terrifying death from his breathing condition.”中，冒号后面的“a terrifying death from his breathing condition”是对前面“the haunting fear of his suffering”这一短语的解释说明。
总结来说，考研英语中冒号的作用主要是引出对前面内容的解释或补充说明，帮助读者更准确地理解句子的含义。