A [Content_Types].xml file includes two types of definitions for the contents of the ZIP package: one for the file types included in the ZIP package and the other for the XML parts.
[Content_Types].xml identifies core content types in the document, such as the main document body, styles, settings, and file properties. As mentioned earlier, this file also identifies file types included in the ZIP package.
Each file type in the ZIP package, including .xml, .rels, and any other files (such as the .png image file referenced in the picture), are identified with a Default Extension
Key content types (usually those for which there is a separate XML part in the ZIP package) are indicated with an Override PartName
reference. The Override PartName is expressed as the path to the XML part within the ZIP package (such as /word/document.xml
Both Default Extension and Override PartName references provide a Content Type definition, as you see in the examples in the picture, which comes from the applicable schema.
Tip You don't need to memorize things like schema references in order to edit parts in a ZIP package; you can simply copy that information from the ZIP package of any document that uses the same content type.