Transliteration is the practice of transcribing a word or text written in one writing system into another writing system or system of rules for such practice.
From a linguistic point of view, transliteration is a mapping from one system of writing into another, word by word. 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.
Transliteration is opposed to transcription, which specifically maps the sounds of one language to the best matching script of another language. Still, most systems of transliteration map the letters of the source script to letters pronounced similarly in the goal script, for some specific pair of source and goal language. (Full article...)