difference between Feature.xml, Manifest.xml, Elements.xml & Onet.xml in SharePoint

• Feature.xml - 
• Defines a Feature 
• Specifies the location of assemblies, files, dependencies, or properties that support the Feature.
• Manifest.xml -
• Used during the deployment of a .wsp solution package.  
• It tells SharePoint what files to copy, what features to install, where to put your binaries, adds SafeControl entries, as well as set code access security.
• Elements.xml -
• This is a definition file for the module. 
• Contains the actual feature element like list instance,  field, Content type, list template, workflow..etc
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•  Onet.xml - 
•  Depending on where an Onet.xml file is located and whether it is part of a site definition or a web template, the markup in the file does some or all of the following:
• Specifies the web-scoped and site collection-scoped Features that are built-in to websites that are created from the site definition or web template.
• Specifies the list types, pages, files, and Web Parts that are built-in to websites that are created from the site definition or web template.
• Defines the top and side navigation areas that appear on the home page and in list views for a site definition.
• Specifies the list definitions that are used in each site definition and whether they are available for creating lists in the user interface (UI).
• Specifies document templates that are available in the site definition for creating document library lists in the UI, and specifies the files that are used in the document templates.
• Defines the base list types from which default SharePoint Foundation lists are derived. (Only the global Onet.xml file serves this function. You cannot define new base list types.)
• Specifies SharePoint Foundation components.
• Defines the footer section used in server email.
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