Perhaps you are asking why people tend to capitalize Word when referring to the Bible even though this is not done in scripture. I think it is a matter of respect for the Bible. In the same manner, many people (myself included) tend to capitalize pronouns referring to God.
DS-11 Application Form for New Passport. Form DS-11. The DS-11 Application Form for New U.S Passport is an application form that should be used when you are applying for a new U.S. passport or when you are replacing an expired U.S. passport that was issued to child under the age of sixteen; Or for a lost passport.
When applying for a US passport renewal, the online form (DS-82) asks you for your Passport Book Number but does not define what this is, exactly. After finding nothing definitive online, I contacted the National Passport Information Center and asked them. (They have a toll free number.