Although some ZIP packages include additional top-level folders (such as for customizations to the Quick Access Toolbar or the Ribbon), every ZIP package includes the _rels folder, the [Content_Types].xml file, and a folder for the main file content (word in this case).
Remember that the folders and files in a ZIP package combine to create a single document. In the ZIP package shown,

The
_rels folder contains a file named
.rels that stores information about the relationships between items in the ZIP package. The .rels file is how the 2007 Office system programs know where to find document components when opening a document. This is an important file to keep in mind when you add or remove content in an Office Open XML ZIP package.

The main document folder, such as the
word folder shown here, stores the main document content, any media (such as pictures) in the document, and various document elements such as settings, headers, and themes. You'll see that the main document folder also contains its own _rels folder, where relationships between elements in the main document folder are defined.

The
[Content_Types].xml file contains definitions of the types of content included in the ZIP package, such as the main document, the document theme, and the file properties. This file also stores definitions of the file extensions used in the ZIP package, such as the file formats (like png or jpeg) of pictures included in a document.
Note The XML files that make up an Office Open XML ZIP package, such as
document.xml, are often referred to as
XML parts or
document parts.
Learn more about the three ZIP package components described here on the screens that follow.