ordinal number

number which indicates a place in a series (first, second, etc.)

In set theory, ordinal, ordinal number, and transfinite ordinal number refer to a type of number introduced by Georg Cantor in 1897, to accommodate infinite sequences and to classify sets with certain kinds of order structures on them. Ordinals are an extension of the natural numbers different from integers and from cardinals.
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Noun
1. the number designating place in an ordered sequence
(synonym) ordinal, no.
(hypernym) number
(hyponym) first, number one, number 1

n. เลขลำดับ (syn. ordinal)