By definition, must the flag stick have a flag attached to its top end?

The definition of a flag stick in golf does not necessitate that it must have a flag attached to its top end. In many casual or recreational play scenarios, the flag stick can stand alone without a flag. This allows players to still have a reference for the hole's location even if a flag is not present. While official regulations may have different stipulations regarding the use of flags in organized tournaments, the general practice allows for flexibility, meaning that a flag is not an absolute requirement for the flag stick itself. Thus, the option indicating that a flag is not mandatory is accurate.