In linguistics, Old Dutch or Old Low Franconian is the set of Franconian dialects spoken in the Low Countries during the Early Middle Ages, from around the 5th to the 12th century. Wikipedia

Set of Franconian dialects spoke in the Low Countries during the Early Middle Ages Wikidata

A branch of Old Low Franconian, with a Frisian substrate, spoken and written during the early Middle Ages (c. 500 - 1150) in the Netherlands and the northern part of present-day Belgium, as well as in areas of northern France along the North Sea coast and adjoining Belgium. This language represents the first attested stage of the Dutch language and its dialects, being succeeded by Middle Dutch in the later Middle Ages. Wiktionary

Language. Wiktionary (translation)