An official passport is a passport which is issued to someone who must travel internationally on official state business. These passports are issued specifically to people who need to travel, rather than to people who are being assigned or posted overseas. For people who are being assigned overseas for state purposes, a diplomatic passport is issued. Official passports are usually a different color from regular passports, to make them easier to identify, and they do not entitle their bearers to any special privileges.
This type of passport is sometimes called a service passport. It is a no-fee passport, which means that people do not need to pay to apply for it. The application for an official passport typically includes all of the materials needed for a regular passport, along with forms which confirm that the applicant needs a passport for official business. Many government agencies which require international travel will assist people with official passport applications.
The official passport can only be used while traveling for official reasons. If someone wishes to travel as a tourist, a tourist passport is required. While it is perfectly legal to carry both, both will require their own visas, and it is important to make sure that visas match up. If someone enters a country with a tourist passport and tries to leave with an official passport, for example, this can cause problems.