SharePoint, the fastest-growing product in the history of Microsoft is a collection of products and software elements which can be configured to run Intranet, Extranet and Internet sites.
WSS stands for Windows SharePoint Services and it is light document management system which helps you to organize your documents inside your organization using file sharing and intranet. MOSS stand for Microsoft SharePoint server and it contain all the things in WSS and more advanced things like people search, workflows, site templates and business intelligence.
There are many applications like Portals, Content Management, Indexing, Search, Business Intelligence and Collaboration built in to SharePoint and Sites, Pages, Lists, Libraries and webparts can be considered as building blocks.
SharePoint most commonly use as intranet portals and it allow users to login to their intranet web site and see the information like announcements and news. Using SharePoint you can build a collaboration environment quickly and easily. That will improve team productivity while managing documents and ensuring integrity of content.