The Green box represents the Raspberry Pi hardware which is running Linux.
Under Linux that are several services (software): Mosquitto MQTT, Node-Red, a Web server, SSH, shell, Progamming Languages, etc.
Here I’ve added the icons for Node-Red and Mosquitto – MQTT Broker. I also have a terminal session with bash, That’s also on the Raspberry Pi. I’ll explain the toaster, radio, ESP board and light bulb in a few slides.