A cookie is a small piece of data stored on a user's device by a web browser while browsing a website. Cookies are used to remember information about the user, such as login details, preferences, and items in a shopping cart. This helps improve the user experience by making websites more personalized and efficient. Tracking cookies specifically collect data about a user's online behavior, such as pages visited and time spent on each page. This information is often used by advertisers to create targeted ads and improve marketing strategies. However, users can manage their cookie settings to enhance privacy.