At present, the passports issued by majority of countries in the world are generally divided into three types: diplomatic, service/official and regular ones. Some countries only issue one type(like UK); some countries only issue two of them (like India, Pakistan and so on); but there are also some countries which issue four or five types (like US, France and so on).
Those who possess diplomatic status are issued a diplomatic type, like the diplomat, consul and official as well as the head of state, governmental officials, delegation members of the Congress or government, who are going abroad for national affairs or activities. According to the international convention, the spouse and the children of the above personnel generally are also issued the same type.
It is issued for government office-bearer of a country. Besides, all countries will issue this type to the staff who works for embassies or consulates abroad but have no diplomatic status, along with their spouse and the grown-up children.
It is issued to all other citizens (populace). For different reasons (line of duty or private affair) for going abroad, the regular one may also have different types in different countries.