Dummy may refer to any of the following:
1. In computing, dummy or dummy data, is a term used to describe a character, document, or file that is used as a placeholder holder for important data. They are useful for both testing and operational purposes. For example, dummy data may be used to fill out variables in software to avoid software testing. Once information is received by a program or entered into the file, the dummy is replaced.
2. Dummy is sometimes used to describe yellow books with information on a vast number of subjects. They are primarily meant for those who are new to the material being presented. For example, the picture is the DOS for Dummies book by Dan Gookin, an example of one of the many iconic dummy books.
3. A dummy is a person who is considered ignorant or foolish.