What is the difference between telehealth, telemedicine, and teleadvice?

Telehealth: A very broad term that refers to a variety of scenarios in which people are communicating about medical issues. Telemedicine, teletriage, teleadvice, and teleconsultations all fall under the umbrella of “telehealth.”
Telemedicine: A type of telehealth practice in which a pet parent communicates with a veterinarian who is able to provide specific diagnoses and prescribe medications. Diagnoses and prescriptions are the hallmarks of telemedicine. Telemedicine is only legal in some states.
Teleadvice: Teleadvice is a service in which a pet parent communicates with a veterinary professional who provides guidance and advice. No diagnoses are made and medications are not prescribed; because of these two important factors, teleadvice is not telemedicine and is - therefore - legal in every state.

Telehealth is the big umbrella for vet care from afar—including teleadvice (guidance only) and telemedicine (diagnoses + prescriptions). Teleadvice is legal everywhere.