A yo-yo is a popular toy consisting of a spool that is attached to a string. When the yo-yo is thrown down, it spins and can return to the hand by pulling the string. This simple mechanism allows for various tricks and techniques, making it enjoyable for both children and adults. Yo-yos come in different shapes, sizes, and materials, including plastic and wood. They can be categorized into two main types: responsive and unresponsive. Responsive yo-yos return to the hand with a gentle tug, while unresponsive yo-yos require more advanced techniques to bring them back.