Here's a great resource from Aeris - an IoT Dictionary.
Aeris Communications has been in the machine-to-machine market for some time and are both a technology provider and a cellular network operator delivering comprehensive IoT / M2M services.
This glossary includes key terms of the IoT (Internet of Things) & M2M (machine-to-machine) communications industry, including wireless and cellular technologies spanning many different markets. It is updated to present current terminology and usage. It's a crowd-sourced resource, so feel free to contact Aries with suggestions.
Also, if you need an IT-related dictionary, I just love WhatIs.com.