What is Yammer? From wikipedia:
Yammer is used for private communication within organizations and is an example of enterprise social software. The tool was originally developed as an internal communication system for the genealogy website Geni. Access to a Yammer network is determined by a user's Internet domain so that only individuals with appropriate email addresses may join their respective networks.

This block uses the embed API to provide a sleek interface and easy setup of the embedded feed within a Moodle course.