MQTT

A communications protocolAn agreed way of doing something. Like a convention, except that protocols tend to be related to processes. designed for small systemsThis is a very generic term for any collection of components that, all together, can do something. Systems can be built from subsystems. Examples are your cell phone; your computer; the radio in your car; anything that seems like a "whole." such as those used for the IoTThe Internet of Things. A broad term covering many different applications where "things"  are interconnected through the internet..