Unified Communication is a comprehensive, tool-based business function focused on uniting hardware, software and services components throughout the enterprise to seamlessly manage communications across multiple devices, applications and geographies.

Social Collaboration is a software-driven business function designed to help improve the way groups, teams, and departments interact and share information in the enterprise to achieve common goals.  Social Collaboration is designed to improve business processes by enabling real-time discussion between groups of people within and organization.

Unified Communications Vs. Social Collaboration

Source: Formicary Collaboration Group