The International Radiotelephony Spelling Alphabet, commonly known as the NATO phonetic alphabet and also known as the ICAO radiotelephonic, phonetic or spelling alphabet and the ITU radiotelephonic or phonetic alphabet, is the most widely used radiotelephonic spelling alphabet. Although often called "phonetic alphabets", spelling alphabets are not associated with phonetic transcription systems such as the International Phonetic Alphabet. Instead, the International Civil Aviation Organization (ICAO) alphabet assigned code words acrophonically to the letters of the English alphabet so that critical combinations of letters and numbers can be pronounced and understood by those who transmit and receive voice messages by radio or telephone regardless of language barriers or the presence of transmission static.