The term slang is used in a very broad and vague sense. Besides denoting low-colloquial (familiar-colloquial) words, it is also used to denote special social jargons/cants, i.e. words typically used by particular social groups to show that the speaker belongs to this group, as different from other people. Originally jargons were used to preserve secrecy within the social group, to make speech incomprehensible to others – such is the thieves' jargon/cant. There is also teenagers' slang/jargon, school slang, army slang, prison slang, etc. See examples of American army slang: to take felt (= to retire from the army, literally – put on a felt hat); fly boy (= pilot); coffin (= unreliable aeroplane); Molotov cocktail (= bottles with explosive materials);