Consciousness itself -- as first person or individual sentient being's subjective experience (or perception of and response to) sensory and memory information -- cannot be explained in objective physical/material terms. Consciousness is wholly described as the stage on which observations and thoughts meet. It is a duality.
Therefore, the following definitions of consciousness is offered -- keeping in mind these limitations:
Consciousness is :
(1) The indescribable first person subjective experience of and response to neurologically or otherwise modulated and stored sensory and/or memory information temporarily reflected in the mind.
(2) The perception and control of the activity of the mind (e.g., thought, concentration, meditation, etc.) -- in conjunction with memory, brain and body -- linked through the senses to the outer world.
(3) The subjective receptive/responsive experience -- whether awake, attentive, inattentive, sleeping, dreaming, or in other alternate states of awareness.
(4) The antonym of unconsciousness -- e.g., when all sensory information is cut off from the subjective experience of qualia by the potentially conscious perceiver.
(5) A ubiquitous, immaterial subjective aspect of total space in conjunction with noumenal objective matter.