Microsoft SharePoint is a web application platform developed by Microsoft according to Wikipedia. I would say it is portal technology developed by Microsoft. SharePoint Server first launched in 2001, and has historically been associated with intranet content management and document management, but subsequent versions like 2010 and upcoming 2013 have significantly broader capabilities.
SharePoint offers business collaboration platform for the enterprise and the Web. Which means that it can empower people and enabling them to connect through an integrated set of rich features. These features are intranet portals, document & file management, collaboration, social networks, extranets, websites, enterprise search, and business intelligence. SharePoint also has capabilities around system integration, process integration, and workflow automation. More general information can be found in TechNet Wiki article SharePoint 2010: Frequently Asked Questions (FAQ).
I myself am active on the TechNet Wiki on integration side with focus on BizTalk Server. There is a great amount of articles on BizTalk Server, yet this also accounts for SharePoint Server. An excellent starting point to get access to SharePoint related articles are:
Now Craig is not the only active contributor for SharePoint Server. Other community members, Microsoft and MVP's like Margriet Bruggeman, Prostakova, Andrea Bichel, dplotnikov, Arun Kumar Arora, and many others have made significant contributions too. These contributions show the dedication of Microsoft and the community for the product SharePoint Server. This dedication not just shows for this product as you also will find a tremendous amount of contributions on the TechNet Wiki for other Microsoft technologies like on my expertise BizTalk Server.