Final answer:
The 'hard problem of consciousness' addresses the question of how subjective experience arises from physical processes in the brain. It centers on understanding qualia and the mind-body interaction, and remains a challenge because subjective experiences are not directly observable or measurable.
Step-by-step explanation:
The "hard problem of consciousness" refers to the challenge of explaining why and how we have qualitative experiences or phenomenal states associated with consciousness. It is distinct from the 'easy' problems of consciousness which deal with the functional and mechanistic aspects, such as memory or vigilance. The hard problem focuses on why, for instance, the sensation of pain has a certain qualitative feel to it, or why the color red appears as it does to us subjectively.
Philosopher David Chalmers coined the term to express this gap in our understanding of how physical processes in the brain give rise to the subjective experience of being. The hard problem persists in asking: how does a non-physical thing, like a sensation or experience, arise from the brain? It questions the nature of qualia, the individual instances of subjective, conscious experience. As such, it also confronts the issue of mind-body interaction: how mental states, seemingly immaterial, affect physical processes and vice versa.
Understanding consciousness in this way stretches beyond the scope of purely objective, scientific inquiry because it delves into the subjective realm that cannot be directly observed or measured. Answers to the hard problem may have profound implications for fields such as artificial intelligence, given the ethical considerations surrounding the treatment of potential conscious machines.