[SerializableAttribute]
public class ContentType : ContentTypeMemberNameFixer, 
	IHydratable

<SerializableAttribute>
Public Class ContentType
	Inherits ContentTypeMemberNameFixer
	Implements IHydratable

Content Types, simply put, are a way of telling the framework what module/functionality is associated with a Content Item. Each product (ie. module) that wishes to allow categorization of data (via Taxonomy or Folksonomy) for it's content items will likely need to create its own content type.

System..::..Object
  DotNetNuke.Entities.Content..::..ContentTypeMemberNameFixer
    DotNetNuke.Entities.Content..::..ContentType