Dual is a grammatical number that some languages use in addition to singular and plural. Wikipedia

A grammatical category used in some languages Wikipedia Disambiguation

Grammatical number that some languages use in addition to singular and plural Wikipedia Disambiguation

Grammatical number found in some languages representing two of an entity Wikidata

In some languages, grammatical number related to precisely 2 objects of the same type (in general, for objects that naturally belong together), as opposed to singular and plural. OmegaWiki

Dual number The grammatical number of a noun marking two of something (as in singular, dual, plural), sometimes referring to two of anything (a couple of, exactly two of), or a chirality-marked pair (as in left and right, as with gloves or shoes) or in some languages as a discourse marker, "between you and me". A few languages display trial number. Wiktionary

Grammatical number of a noun marking two of something. Wiktionary (translation)