Awareness is what knows that this word is being read. It is not a thing one finds on introspection; it is that in which every finding occurs.
In Dzogchen it is called rigpa — the cognizant, open quality of mind. In Advaita it is chit — pure knowing, one of the three aspects of Brahman (being, consciousness, bliss). In direct-path teachings it is invited to recognize itself — awareness looking at awareness.
Whether awareness is a faculty of the brain or the ground of everything is one of the oldest and most active questions in both philosophy and cognitive science.