IoT Hub is an IoT Platform as a service, it sits between connected devices and business-specific software.
Connected devices is the common name for all devices able to communicate over the Internet (via Wi-Fi or 4G for instance). Connected devices are everywhere and can be used in a very broad range of applications. They can be smartphones, doorbells, light bulbs, refrigerators, cars, TVs, … even a web browser can act as a connected device!
MQTT is a lightweight and standardized publish/subscribe messaging transport protocol, designed for low-power usage, minimized data packets, and efficient distribution of information to one or many receivers. MQTT supports secure communication using TLS and it is often used in IoT use cases.
All kinds of connected devices supporting the MQTT protocol can be connected to IoT Hub. MQTT through WebSockets is also supported. There is no limitation to specific vendors.
To learn more about what is a Hub, what is a Device and what is a Route, head over to our dedicated pages: