Any number term of the form first, second, third, twenty-fifth or five hundredth. The English ordinals are usually called as adjectives.
A counting number.
Examples are: one, two, three, four, seven, twenty etc.
After a noun we usually use a cardinal number instead of an ordinal number. This structure is common in titles.
the fourth book – Book Four
the third act – Act Three
However, the names of kings and queens are said with ordinal numbers.
Louis XIV: Louis the Fourteenth
Elizabeth II: Elizabeth the Second