A term used in psychology and linguistics for children raised in such isolation that they never acquire language. There have been two famous well-documented cases in the last two-hundred odd years: a boy, Vincent, who lived in the woods of Southern France, and a girl, "Jeannie", who was kept locked in a room and tied to a potty chair by her abusive parents for the first twelve years of her life in 70s LA.
Vincent was sent to the French Academy for Deaf-Mutes, where Enlightenment-era scientists attempted to teach him language, and meticulously documented their largely negative results. The experiences of the Vincent were made into a movie, L'enfant Savage, by Truffaut, which was ironically released less than a week after Jeannie was discovered by the authorities in Los Angeles.
Jeannie was given to the care of large team of linguists, psychologists, sociologists, neurologists, and miscellaneous social scientists trying to pick up crumbs of the NIMH grant and prestige that her case entailed, though they had not much more success than their French forbears.
In both cases, the children succeeded in rapidly acquiring a relatively large vocabulary1much more quickly than a child learning their first language for the first time would have, but never had any success at all in mastering the structural elements of language (i.e. grammar and syntax). If Jeannie wanted to say something like "We should go to the store to buy butter.", she would have said something like "store butter buy go". Interestingly enough, she seemed much more at home communicating in ASL, which she was also taught bits of.
There are some strange correlations between Jeannie's and Vincent's recorded behavior. Both seemed completely immune to the uncomfortable effects of cold: Vincent would happily play, stark naked, in waist-deep snow, and Jeannie would always draw her baths freezing cold if she had the choice. Both hoarded glasses full of water and liquids. Both seemed to have an almost unexplainable effect on people they met, even ones who knew nothing of their fantastic life-stories, predisposing them to want to help and be friends with the children they saw.
Neither case ended happily. When it became clear that Vincent was going to learn no more French, he was discharged from the Deaf-Mute academy and given to a family of servants, where he lived a dreary life and died in his forties. Once the NIMH money dried up for the study of Jeannie, she was sent to a series of unpleasant foster homes, actually briefly remanded to the care of her mother, and eventually sent to a Southern California adult-care group home, where she lives today.
1 Tem42 tells me that Vincent's vocabulary actually was never very large. None of the sources I have tell me exactly how many words either of the children knew, and it's not really clear what would constitute a large or small vocabulary in a case like this. I think it can safely be said that both probably knew more words than a child of two or three first acquiring language would, but far less than a normal person of their age. Vincent may even fall below the low end of that -
wild boy of Averyon says he "never learned more than a few words", which I
think is on the low side of accurate, but I'm not totally certain.