Microsoft Communicator 2011 is used by Microsoft Office to allow instant messaging, audio chatting and video/web conferencing.
Microsoft Communicator 2011 is essentially a Microsoft branded instant messaging client designed for businesses, and is a progression from Microsoft Messenger but it offers far more power and features.
Microsoft Communicator 2011 can handle everything from instant messaging to telephony, video chatting and teleconferencing. Not only that, thanks to Microsoft Communications Server or Lync (the hardware infrastructure needed to use Communicator) it can support multiple IM protocols meaning you can communicate with those using Windows Live Chat, Yahoo and Jabber. This is a big advantage over Microsoft Messenger which is "closed" to protocols other than Microsoft Messenger.
Microsoft Communicator 2011 allows Mac users to communicate and collaborate with Office Windows users and of course features complete integration with Microsoft Outlook (now available for Mac) and every other component of Microsoft Office for Mac 2011. For example, the status options of Microsoft Communicator 2011 are set automatically according to your Outlook calendar (and manually), and you can start communicating with your contacts in Microsoft Word 2011, Microsoft Outlook 2011andMicrosoft PowerPoint 2011.
Microsoft Communicator adds much needed communication features to Microsoft Office for Mac.