Content types are a site-scoped Feature.

Features are a way of encapsulating Windows SharePoint Services functionality for ease of distribution and deployment. Features provide a mechanism by which developers can package the files a solution needs, such as content types, Web Parts, lists, and site definitions. Developers package the necessary files into a .wsp file, which is essentially a .cab file containing a manifest that lists its contents.

Inside the Feature, the feature.xml file contains references to all the element manifests within that Feature. Content type definitions are element manifests. You must create a content type definition for each content type included in your Feature.

For more information on content type definitions, see Content Type Definition Schema.

Note:
Site content types defined in one Feature can reference columns or content types contained in another Feature. In such a case, make the Feature referencing the contents of another Feature dependent on that Feature.

For more information about Features, see Working with Features.

Important:

Under no circumstances should you update the content type definition file for a content type after you have installed and activated that content type. Windows SharePoint Services does not track changes made to the content type definition file. Therefore, you have no method for pushing down changes made to site content types to the child content types. For information about best practices when making changes to content types that have been installed and activated, see Updating Content Types.

Other Resources