The act or state of knowing.
By reason of its primordial character knowledge cannot be strictly defined, but only described.
Philosophically the term implies the consciousness of any object which can be attained by the cognitive faculties, whether this be simply the consciousness of sense experience, or the understanding of general laws and principles.
The latter, considered as the fruit of a demonstrative process of reasoning, is properly termed science.
From a psychological point of view, knowledge is effected by the vital union of an object with a knowing subject.
New Catholic Dictionary