Transliteration is the practice of transcribing a word or text written in one writing system into another writing system. It is also the system of rules for that practice. Technically, from a linguistic point of view, it is a mapping from one system of writing into another. Transliteration attempts to be exact, so that an informed reader should be able to reconstruct the original spelling of unknown transliterated words. To achieve this objective transliteration may define complex conventions for dealing with letters in a source script which do not correspond with letters in a goal script. Romaji is an example of a transliterating method.