The main difference is what is included in the package. Since there are no set parameters for packaging options in this hobby, different manufacturers may vary their definitions of what is included.
KIT indicates that all the foam pieces along with the crucial components of aesthetic appearance are included in the package. Some on-board electronics may be included with a KIT such as the electric retracts and will be noted on the specifications of the model. Note that this packaging option is recommended for advanced individuals with knowledge in customizing their onboard electronic components or for those not intending to fly this model.
ARF indicates that all the foam pieces along with the crucial components of aesthetic appearance and electronic components are included with the exception of the battery, balance charger, and radio system (transmitter and receiver). Most on-board electronics are pre-installed by the manufacturer. Note that this packaging option is recommended for those who already own a radio system, battery and balance charger.
RTF includes all the foam pieces along with the crucial components of aesthetic appearance, electronic components, battery, balance charger and radio system unless noted otherwise. Most on-board electronics are pre-installed by the manufacturer. Note that this packaging option is recommended for beginners or first-time pilots. Be aware of balance charger accessories that are not included (wall adapters usually sold separately). Advanced models with the RTF option may or may not come with a battery or charger. Please read the ‘Package Includes’ area carefully under the item’s for clarification of what is included with the package. | 
