undefined symbol

An undefined symbol is a symbol (name or identifier) used in a program or library that has not been defined or declared. This can happen when a function, variable, or other identifier is referenced but not properly defined. The linker may be unable to find the definition of the symbol if it is not provided by a library or object file. This can result in a linker error or a runtime error when the program tries to use the undefined symbol. To resolve this issue, the missing symbol needs to be defined or declared in the appropriate location.