Sharepoint solution file
WSP is a file extension for a solution file used by Windows. WSP stands for Windows Sharepoint. WSP files are CAB files containing a set of features, site definitions, and assemblies that can be applied to a group of computers. WSP files are reusable and easily distributable; different features of the “Solution” can be enabled or disabled selectively.
Learn more about .WSP files:
SearchWinDevelopment.com provides this introductory guide to Sharepoint.
See 'Deploying a Solution' at MSDN.
Find out about Microsoft Sharepoint at ITKnowledgeExchange.com.