Cookies are small text files that are saved on your computer when you view certain web pages. Cookies are used for a wide variety of purposes, e.g. to personalise web pages, to enable online shopping to work correctly, or to monitor how many people use a website and collect information about them.
You can tell your browser not to accept cookies if you wish, though this may mean some websites won't work properly. You'll find instructions on how to control cookies on the AboutCookies website or you can view your browser's online Help.