Phonetic representation
Phonetic representation, or more commonly phonetic transcription is the representation of speech sounds using symbols in phonetic alphabet such as IPA, X-SAMPA, Kirshenbaum for linguistic studies (especially phonetics, phonology and speech processing) and for learning the pronunciation of languages. Among these systems, the International Phonetic Alphabet has been the most widely used so far, whose symbols are printed in most dictionaries and books on linguistics.
The necessity of phonetic representation
In all languages, the letters in the orthography do not always have a one-to-one correspondence with the speech sounds in the pronunciation of words. This fact is not of great importance to native speakers of a particular language, but in case of foreigners who don't learn pronunciation with phonetic symbols and rely only on their teachers, or their "guesses" on the orthography, wrong pronunciation will go along with them during the entire study. For languages whose orthography does not tell much about sounds, e.g. English, or whose many letters are silent, e.g. French, phonetic transcription is crucial not only for learners but also for linguists. For example, in the word "scissors", the digraph "sc" stands for /s/, the double s ("ss") for /z/, and the letter "r" is silent in British English. Another noteworthy example is the word "colonel", which is not pronounced /ˈkɒlənɛl/ but /ˈkɜːrnəl/.