What is the difference between IoT and M2M?

M2M (Machine-to-Machine) refers to direct communication between devices, often a device sending data to a central system over a cellular SIM — like a vehicle tracker or a smart meter. IoT (Internet of Things) is the broader concept of connected devices, sensors and platforms working together over the internet. In practice the terms overlap; on connectivity, M2M usually means the SIMs and networks that link your devices.