What's the meaning of "blue blood"?

What's the meaning of "blue blood"?
What's the meaning of "blue blood"?

What's the meaning of "blue blood"?
贵族血统；出身贵族

Blue talk is language or a topic which is not fit for polite “blue” to describe something profane dates from around the 1800s, but

固定词组:贵族血统;贵族阶级;贵族
字面意思：蓝色的血 实际意思：贵族出身的人
黑血液
贵族出身