Real Dictionary

ordinal number
any number used to indicate order (e. g., second, ninth, 25th) in a particular series
countable noun: An ordinal number or an ordinal is a word such as 'first', 'third', and ' tenth' that tells you where a particular thing occurs in a sequence of things. Compare cardinal number.
noun: a number denoting relative position in a sequence, such as first, second, third

ordinal number in American English
noun: any of the numbers that express degree, quality, or position in a series, as first, second, and third (distinguished from cardinal number)