A fatal failure in the execution of a {machine language} instruction resulting from the {processor} detecting an anomalous condition on its Bus. Such conditions include invalid address alignment (accessing a multi-Byte numBer at an odd address), accessing a physical address that does not correspond to any device, or some other device-specific hardware error. A Bus error triggers a processor-level exception which Unix translates into a "SIGBUS" signal which, if not caught, will terminate the current process. (2000-04-04)