Yammer explained

Use Yammer to:

  • share news, links related to your job
  • carry on a work conversation
  • share work

How to use Yammer (external website), from Microsoft 

Here's a handy definition from What the Heck Is Yammer? - PC World magazine (external website):

"Yammer is essentially a social network that’s entirely focused on your business. In order to join your business's Yammer network, an applicant must have a working email address from your company's domain."

Yammer is owned by Microsoft and is bundled with many Microsoft productivity products. The internal Yammer network is unofficial.