The meaning depends on context. In hardware, it is common to depend on 'undefined', but stable and predictable behavior. In case of C standard, there is separat

The meaning depends on context. In hardware, it is common to depend on 'undefined', but stable and predictable behavior. In case of C standard, there is separate 'undefined' and 'unspecified' (and also 'implementation-defined'). And 'undefined' is allowed to be unpredictable and inconsistent, because it is just invalid usage.