Unified Communication refers to the idea of consolidating multiple communication channels used within an enterprise to form a single interface for each user.
Unified Communication means that services such as the company's email system, its enterprise social network, fixed voice lines, mobile voice lines, whiteboard sharing apps and chat apps as well as webRTC communication services used, are all integrated such that a single common identity for a user is used across all these services, regardless of the hardware, technology and applications deployed.
It also means that the communicated content is accessible from multiple points, for example, an SMS message also appears on the enterprise chat application as well as the enterprise email.