What is the Office Button?

In Office 2007, the Office Button is located at the top left corner of all applications. Clicking it opens a menu containing frequently used file-level commands (e.g., Open, Print, and Save) previously available in the File menu. The Office Button is a circle with the Office logo:

MS Office 2007 Logo Button
Office Button (Office 2007)

The options available in the Office Button menu are:

New Creates a new document
Open Opens an existing document from disk
Save Saves the open document to disk
Save As Saves the open document to disk under a different name
Print Prints the open document
Prepare Prepares the document for distribution, through such tasks as adding a signature or encryption
Send Sends the document to another user by email or fax
Publish Makes the document publicly available via a document server or a public web space
Close Exits the open document

At the bottom of the menu are two buttons, labeled to match the application: an options button (e.g., Word Options, Excel Options), where you can change settings for the application, and an exit button, which will close the application entirely.