A feature is a type of enhancement that can be plugged into SharePoint. Custom features can be written by developers, but SharePoint itself is built on features as well. For example, many of the capabilities found in SPS are implemented as features that aren’t present in SPF. This makes sense since SPS adds many enhancements on top of SPF.
Features can be used for many types of functionality, such as adding or removing menu commands, creating lists, creating content types, even altering the SharePoint interface using custom ASP.NET controls.
Each SharePoint feature has a defined scope. The scope gives users flexibility in determining where the enhancement is used. Four scopes are available: