Question: I'm familiar with the kind of cookie that tracks user preferences and browsing histories. But what's a supercookie?
Answer: Yes, there are many more kinds of cookies these days than chocolate chip or oatmeal raisin. As you correctly stated, a regular cookie is a bit of text stored on your browser that tracks user preferences and browsing histories. Cookies enable websites to "remember" information about you such as your name, preferences, and shopping basket contents.
Recently, some major online properties have been identified as using supercookies, also known as "Flash cookies" and "zombie cookies." Supercookies serve the same basic purpose as regular cookies but are stored in different locations on a user's machine — for example, in a file used by a plug-in such as Flash. This makes them harder to find and delete, especially since a browser's built-in cookie detection process won't remove them. Furthermore, some supercookies have additional capabilities, like regenerating regular cookies to prevent their removal by the user.