Short answers, pulled from the story.
Consciousness is being aware of something internal to oneself, or of states or objects in one's external environment. It has been the subject of explanation, analysis, and debate among philosophers, scientists, and theologians for millennia, with no consensus on what exactly should be studied or whether it is a scientific concept.
The words "conscious" and "consciousness" date in English to the 17th century, with the first recorded use of "conscious" applied figuratively to inanimate objects in 1643. They derive from the Latin conscius, combining con, meaning "together," and scio, "to know," originally meaning knowing something with another person, especially sharing a secret.
The modern concept is often attributed to John Locke, who defined the word in his Essay Concerning Human Understanding, published in 1690, as "the perception of what passes in a man's own mind." His definition shaped 18th-century British philosophy and appeared in Samuel Johnson's Dictionary of 1755.
The hard problem of consciousness was named by David Chalmers and concerns how mental experience can arise from a physical basis. Chalmers argued that access consciousness can in principle be understood in mechanistic terms, but that phenomenal consciousness, the raw felt quality of experience, is far more challenging to explain.
The neural correlates of consciousness are the brain activity strongly predictive of conscious awareness, studied using imaging techniques such as EEG and fMRI. Activity in primary sensory areas like the primary visual cortex is not sufficient for consciousness, and a top-down flow of activity from the frontal cortex to sensory areas predicts awareness better than a bottom-up flow.
Opinions are divided. Thomas Henry Huxley argued consciousness is a causally inert by-product of neural activity, while William James reasoned that natural selection preserving consciousness implies it had survival value. Some theorists favor an exaptive account in which consciousness arose as a by-product of other changes, such as increases in brain size, rather than as an adaptation.
The mirror test is an operational test for self-awareness developed by Gordon Gallup in the 1970s. A spot of coloring is placed near the forehead, and an animal passes if it touches or tries to remove the spot, indicating self-recognition. Humans older than 18 months, other great apes, bottlenose dolphins, orcas, pigeons, European magpies, and elephants have passed it.