SharePoint solution is deployed to a SharePoint server by using a solution package (.wsp) file. You can use Visual Studio to organize your SharePoint Project Items into Features and to create a package to deploy your SharePoint Features.
A solution package is the distribution package (file extension .wsp) that delivers your custom SharePoint code and artefacts to the web servers within your server farm.
Components that can be distributed in a solution package include:
- .NET Framework assemblies that contain the code that drive the solution.
- Deployment files such as resource files, images, or other helper files.
- Many solutions involve the delivery of new templates and definitions for sites, lists, libraries, fields, content types, and more. These definitions are in the form of CAML-based XML files.
- Configurations that must be performed at the Web-server level — for example to the web.config files for the registration of Web Parts.
Reference (2012-03-17): http://technet.microsoft.com/en-us/library/cc263289(v=office.12).aspx