The nature of knowledge and what it means to “know” something is a central question in epistemology, the branch of philosophy concerned with the nature of knowledge, belief, and justification. Various theories of knowledge exist, but one commonly accepted definition is that knowledge is justified true belief. In other words, to know something, an individual must believe it to be true, the belief must be justified by evidence or reasoning, and it must actually be true. However, this definition has been the subject of debate and refinement. Philosophers have explored the nature of justification, the role of skepticism, and the reliability of different sources of knowledge, such as perception, reason, and testimony. Additionally, the question of whether knowledge is absolute or subject to revision and uncertainty is a matter of ongoing philosophical inquiry.