An abend (a combining of two words, abnormal end, when operator messages were as short as possible) is an abnormal, rather than planned, end or termination of a computer program because of some problem with how it is running. For example, the program may have attempted to address some computer memory space that it was not given the right to address. This term is more common in older mainframe systems than in PC systems.
When used, abend usually refers to the abnormal end of an application program because of application errors. Failure of the operating system is usually called a crash. In smaller systems, the term crash is applied to both application program and operating system failure. A crash also can be caused by hardware failure.