An error that causes a program to abort, regardless of the programming language.
A fatal error causes the program to finish execution, usually returning back to the operating system. This broad category also covers errors that are not thrown as exceptions.
When using this tag, it may be a good idea to add more focused tags like outofmemoryerror, panic and the like.
Be sure to leave the language's tag (for example php, c or vb.net) so others can easily know if they can help you.