## ORDINALNUMBER

### Ordinal number

In set theory, an ordinal number, or just ordinal, is the order type of a well-ordered set. They are usually identified with hereditarily transitive sets. Ordinals are an extension of the natural numbers different from integers and from cardinals. Like other kinds of numbers, ordinals can be added, multiplied, and exponentiated.

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### ordinal number

#### Noun

1. A word that expresses the relative position of an item in an ordered sequence.
First, second and third are the ordinal numbers corresponding to one, two and three.
2. A number used to denote position in a sequence.
In the expression a3, the "3" is an ordinal number.
3. A generalized kind of number to denote the size of a well-ordered set.

The above text is a snippet from Wiktionary: ordinal number
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