What is MQTT (Message Queues)? Well I could write up and down about just that subject, but other people have done that before and are properly better at explaining it than me. Google it (Heck use Bing if you are feeling lucky today).
Lazy? Okay then. It is a small footprint protocol on top of the TCP/IP protocol and is for sending information. Mostly used on embedded devices (IoT) where CPU power is limited. You can not have an Intel octa-core powerhouse, when it has to run for a year on a coincell battery.
REST is not an option, it is way to resource heavy for simple sensor data.