This review aims to clarify four perennial issues surrounding the concept of curiosity: its nature, conceptual distinction from situational interest, types, and educational implications. First, we argue that humans have evolved to be deeply curious to adapt to a world of uncertainty. Curiosity can be likened to an appetite for knowledge which can be satiated by specific information that fills a knowledge gap. Information-seeking behavior is determined by the expected availability of information using a cost-benefit analysis. Second, although curiosity and situational interest are often considered synonyms, we show that the two constructs differ in terms of their theoretical account, biological underpinnings, triggering factors, emotional valence, specificity of information searches, and relationship with individual interest. Unlike situational interest, which is the positive affect triggered by a wide variety of sources (e.g., autonomy, relatedness, competence), curiosity is an aversive cognitive state caused by an information gap. Situational interest follows the hedonic principle and is associated with opioid liking system in the brain. Curiosity, by contrast, is understood through drive theory and involves dopaminergic wanting system. Situational interest drives individuals to approach the stimulus while curiosity promotes the active seeking of missing information. Iterative cycles of curiosity resolution can lead to the development of individual interest. Third, we introduce two types of curiosity: curiosity for "what" (forward curiosity) is provoked by unpredictability, whereas curiosity for "why" (backward curiosity) arises from incongruity. Finally, driven by the unique characteristics of curiosity, we suggest ways to design learning environment that can nurture students' curiosity.