The Zone of Proximal Development (ZPD) is a concept introduced by psychologist Lev Vygotsky, referring to the difference between what a learner can do without help and what they can achieve with guidance and encouragement from a skilled partner. It emphasizes the importance of social interaction in the learning process, suggesting that learning is most effective when it occurs within this zone, where tasks are just beyond the learner's current abilities but achievable with support.