All of the things you mentioned are potential components or application within Unified Communications. However, UC is not static and can not be adequately defined by listing its specific functions, components or attributes.
Here is my definition:
Unified Communications is an evolving communications technology architecture which automates and unifies all forms of human and device communications in context, and with a common experience.
Its purpose is to optimize business processes and enhance human communications by reducing latency, managing flows, and eliminating device and media dependencies.
Rick McCharles
http://www.ric.ca/blog
