It comes from Nagel's famous paper "what is it like to be a bat?"
He argues that something is conscious only if there is "something it is like" to be that thing. "Something it is like" meaning an answer to a question like "what was it like to speak on stage for the first time?", implying that there is some subjective character to the experience.
He argues that something is conscious only if there is "something it is like" to be that thing. "Something it is like" meaning an answer to a question like "what was it like to speak on stage for the first time?", implying that there is some subjective character to the experience.