The use of tanru or lujvo is not always appropriate for very concrete or specific terms (e.g. 'brie', or 'cobra'), or for jargon words specialized to a narrow field (e.g. 'quark', 'integral', or 'iambic pentameter'). These words are in effect 'names' for concepts, and the names were invented by speakers of another language. The vast majority of names for plants, animals, foods, and scientific terminology cannot be easily expressed as tanru. They thus must be 'borrowed' (actually 'taken') into Lojban from the original language, forming words called fu'ivla. The word must be Lojbanized into one of several permitted fu'ivla forms. A rafsi is then attached to the beginning of the Lojbanized form, usually using a vocalic consonant as 'glue' to ensure that the resulting word doesn't fall apart. The rafsi categorizes or limits the meaning of the fu'ivla; otherwise a word having several different jargon meanings in other languages (such as 'integral'), would require a choice made as to which meaning should be assigned to the fu'ivla. fu'ivla, like other brivla, are not permitted to have more than one definition.