Definition
Consciousness is the first-person experience of mental states — the sense that there is something it is like to be a particular subject from the inside. Philosophers distinguish phenomenal consciousness (the qualitative feel of experience, like the redness of red) from access consciousness (the availability of information to reasoning, reporting, and behavior).
In Gödel, Escher, Bach and his later I Am a Strange Loop, Hofstadter argues that consciousness is what a brain with a self-symbol feels like from inside — the experiential face of a strange loop running in neural tissue. The view is neither dualist (no extra substance) nor eliminativist (consciousness is real, not a fiction); it is structural.
Why it matters
How it works
The strange-loop account: a brain rich enough to model itself contains a self-symbol — an active pattern that represents the system it is part of. The self-symbol's activity is modulated by other symbols and modulates them in return. Because the self-symbol is one of the symbols whose activity it influences, the system has a closed loop across levels — a strange loop. Consciousness is what this loop "feels like" from inside the system that supports it.
This does not solve the hard problem in the strong sense of explaining why structure should feel like anything. It does relocate the question: from "what makes neurons conscious?" to "what kind of structural pattern, in any substrate, supports the experience of being a self?" The answer Hofstadter proposes is the strange loop. Different proposals (integrated information theory, global workspace theory, higher-order theories) carve the space differently but share the move of looking for structural rather than substantial answers.