Gettier cases are philosophical scenarios that challenge the traditional definition of knowledge as justified true belief. According to this definition, for someone to know something, three conditions must be met: the belief must be true, the person must believe it, and there must be justification for that belief. However, Edmund Gettier, a philosopher, presented examples where these conditions are satisfied, yet intuitively, knowledge seems to be absent. These cases illustrate that having justified true belief does not necessarily equate to knowledge, prompting further exploration into the nature of knowledge in epistemology.