Rindfleischetikettierungsüberwachungsaufgabenübertragungsgesetz means "law for the delegation of monitoring beef labelling." This 63-letter word is no longer a part of the German language:
Professor Anatol Stefanowitsch, a linguistics expert at the Free University of Berlin, told the German news agency dpa that the beef labelling law was the longest "authentic" word in the German language.
The law was considered a legitimate word by linguists because it appears in official texts, but it never actually appeared in the dictionaries, because compilers of the standard German dictionary Duden judge words for inclusion based on their frequency of use.
At the link, you can listen to an audio recording of someone saying the word.
(Photo: Naotake Murayama)