Scaffolding is where children work together to complete a task, as more advanced kids help the less-advanced learn how to do the task. However, Vygotsky never used the term "scaffolding;" instead he used the phrase the "Zone of Proximal Development (ZPD)."
The ZPD is the difference between what a child can do without help and what the child can do with help from someone else. The idea is that once a child completes the task with the help of another student, the child has learned how to do it. Therefore, the child can then complete the task without help, once the "scaffolding" of another learner helping with the task has been removed. Adults can also provide scaffolding for children as they walk them through tasks.