How is 'consciousness' (vinyaana) defined in Buddhist texts?
'It cognizes, it cognizes': Thus, friend, it is said to be
'consciousness.' And what does it cognize? It cognizes 'pleasant.' It
cognizes 'painful.' It cognizes 'neither painful nor pleasant.' 'It
cognizes, it cognizes': Thus it is said to be 'consciousness.' - MN 43


And what, bhikkhus, is consciousness? There are these six classes of
consciousness: eye-consciousness, ear-consciousness,
nose-consciousness, tongue-consciousness, body-consciousness,
mind-consciousness. This is called consciousness. - SN 12.2


The six classes of consciousness should be understood. ’ So it was
said. And with reference to what was this said? Dependent on the eye
and forms, eye-consciousness arises; dependent on the ear and sounds,
ear-consciousness arises; dependent on the nose and odours,
nose-consciousness arises; dependent on the tongue and flavours,
tongue-consciousness arises; dependent on the body and tangibles,
body-consciousness arises; dependent on the mind and mind-objects,
mind-consciousness arises. - MN 148