Today it means: A court order allowing a plaintiff to go to someone's premises and seize documents (entry must be with that person's permission, but if refused would be a contempt of court). Used in extreme cases when a prospective defendant might destroy documents, especially computer files, if they knew a court case was coming. Full definition →
Named after the 1976 British case of Anton Piller KG v Manufacturing Processes Limited, a leading case on the issuance of such orders (Anton Piller KG, the plaintiff and party requesting the order, was a German manufacturing firm).
Etymology from Wiktionary, CC BY-SA 4.0.