A patroniem is the Dutch word for ‘patronymic,’ a name derived from the father’s name. Examples are Jansen (son of Jan), Marijnissen (son of Marijn or Marinus) or Damen (son of Daam or Adam).
In some provinces where patronymics were common, like Friesland and Noord-Brabant, you may encounter the word patroniem in search engines. If this is the case, be sure to use try that field, because you will not get any results by searching for a patroniem in the achternaam (surname) field.
See the article about patronymics for more information about patronymics in the Netherlands.