An error message is a message isplayed when an unexpected condition occurs, usually on a computer or other device. Error messages are often displayed using dialog boxes. Error messages are used when user intervention is required, indicate that a desired operation has failed, or give very important warnings such as being out of hard disk space. Error messages are pervasive throughout computing, and are part of every operating system, or computer hardware device. Proper design of error messages is an important topic in usability and other fields of human-computer interaction.