Telemedicine encompasses medical practice, teaching, and research with real-time interactions over distances too great for unaided communication. It includes audio and video transmissions, either separately or combined, and can be done through mechanical (e.g., signal flags or lights) or electronic means (e.g., telecommunications). In many ways, telemedicine is a subset of medical informatics, itself a rapidly developing field. Prior definitions have been broader, including not only medical practice over distance, but also simple information transfer.