Quaclappen is an archaic Dutch word that originally meant to gossip or slander. In genealogy, you may come across the term in court records, as the summaries of verdicts in civil cases.
I have mostly come across the term in Friesland, where the index of quaclappen for 1527-1591 are available via Alle Friezen. Transcriptions for 1600-1620 are available via Tresoar.