Yammer is a private social network for organisations and is built around open communication. For example, you can use it to efficiently resolve support issues, gather feedback on projects and documents, and spread best practices. Yammer groups are a place where members can get up to speed on a project, participate in threaded discussions, and loop customers and vendors into conversations. Yammer also helps you discover relevant information, groups, files, and people so everyone can share their knowledge across departments.

Getting Started With Microsoft

Visit the Microsoft website here for a more complete introduction to Yammer.