Flash cookies, aka Local Shared Objects (LSOs), are small files stored on users’ computer by websites using Adobe Flash applications.
Flash cookies are used for purposes very similar to those of regular cookies. They can be used for storing scores and preferences of Flash gamers or to store preferences relative to Flash video players (on YouTube for instance).
Technically different, Flash cookies are not erased when erasing cookies and are less easily acessible. For this reason Flash cookies are sometimes used for creating zombies cookies.