To spatchcock a chicken, or butterfly it, is to remove the backbone, thus allowing it to be completely opened out and flattened. Doing this reduces the cooking time significantly and allows the whole bird to be cooked in different, speedier ways, such as grilling or pan frying.
Why spatchcock? Crispy skin and shorter cooking time! The even shape makes it easier to cook, and with the heat hitting all sides more evenly, you get maximum crispy skin coverage.