Software rot

The term software rot refers to the observation that computer programs appear to decay in their performance and reliability over time, even if nothing appears to change. That’s because all computer programs have dependencies on other computer systems – at least an operating system, and perhaps additional dependencies such as system utility programs and other applications – and those external dependencies will themselves change over time.

Therefore, all software must be continually maintained to keep it working, else software rot will set in.

See also [technical debt], which is a different but related concept. A system that has high technical debt is more likely to suffer from faster rot.