What is the ordinal number?
An ordinal number is an adjective derived from a number that describes an object's position in a sequence.
(see here for more detail)
With some exceptions (listed below), ordinal numbers are created by adding -th to the end of a cardinal number (ordinary numbers). For example:
In context: There are ten cards numbered in order. This one has the number 'six' on it. It is the sixth.
Irregular ordinal numbers: