Wiktionary
n. (context computing English) A message displayed when an unexpected condition occurs, usually on a computer or device.
Wikipedia
An error message is information displayed when an unexpected condition occurs, usually on a computer or other device. On modern operating systems with graphical user interfaces, error messages are often displayed using dialog boxes. Error messages are used when user intervention is required, to indicate that a desired operation has failed, or to relay important warnings (such as warning a computer user that they are almost out of hard disk space). Error messages are seen widely 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.
Usage examples of "error message".
On the center screen, right beneath the error message, the VR painted a terrifying image.
It tried to look up the error message in its error message look-up table and couldn't find that either.
For some reason he was getting a consistent error message whenever he tried to turn on a grid.
For the thousandth time, she inserted the plastic chip into its slot, saw the error message appear, and knew just how big a fool she had been.
Again, the installation died without any error message or explanation.
The best I could get was a brief surge of random text-and then an error message from the software itself.
Again the error message flashed but could not overcome the angelic announcement.