What is SharePoint?
Microsoft Office SharePoint Server 2007 is an integrated suite of server capabilities that can help improve organizational effectiveness by providing comprehensive content management and enterprise search, accelerating shared business processes, and facilitating information-sharing across boundaries for better business insight. Additionally, this collaboration and content management server provides IT professionals and developers with the platform and tools they need for server administration, application extensibility, and interoperability.
# Passage from Microsoft SharePoint web site and resources you can get almost everything from here.
You can refer official or useful urls here.
1. Microsoft Office Online > Products > Microsoft Office SharePoiknt Server
2. SharePoint Magazine