An unreferenced variable in the source code of a computer program is a variable that is defined but which is never used. This may result in a harmless waste of memory. Many compilers detect such variables and do not allocate storage for them (i.e., "optimize away" their storage), generally also issuing a warning as they do.[1]
Some coding guideline documents consider an unreferenced variable to be a symptom of a potential coding fault. On the other hand, unreferenced variables can be used as temporary placeholders to indicate further expected future developments in the code.