Lync is Microsoft's Unified communications Solution. Providing IM & Presence, Video conferencing, Enterprise voice, Office integration and Mobile apps as clients (iOS, Android, WP7, Symbian).
Any questions related to Lync clients, Lync Server, Lync integration tools, Lync Online (Office 365) can use this tag.
Definition from Microsoft's Lync product page Lync Microsoft® Lync® is an enterprise-ready unified communications platform. With Lync, users can keep track of their contacts’ availability; send an IM; start or join an audio, video, or web conference; or make a phone call—all through a consistent, familiar interface. Lync is built to fully integrate with Microsoft Office. The Microsoft Lync 2010 desktop client is available for Windows and for Mac and mobile versions are available for Windows Phone, iPhone/iPad, and Android devices.