Indeed, a whole branch of philosophy is given over to questions about knowledge. On the other hand, knowledge is a word we all use and understand in everyday life without much trouble. Sometimes it is very difficult to make tacit knowledge explicit, which you need to be able to do to understand, explain, test or teach it. The deep knowledge has become tacit. Knowledge is formulated in the minds of individuals through experience.
People learn, naturally, all the time.
Knowledge is shared between groups and communities through shared experience and through the transfer of knowledge, both tacitly and explicitly. Every individual and community has a pool of general and specific knowledge. Every task or skill has specific knowledge associated with it. Despite the vital nature and value of knowledge, its apparent intractability has meant that it has not, in the past, received the direct attention of management that it deserves and needs. Knowledge has usually been only indirectly managed through human resources and information technology initiatives.