Phonetic language has been studied as far back as 2,000 years ago by Sanskrit scholars, such as the grammarian Panini who taught pronunciation so that ancient rituals could be exactly enacted and preserved in their natural, original state. In 1653, an English mathematician John Wallis was the first to classify vowels according to their place of articulation. German Herman Helmholtz published The Sensations of Tone in 1863 and inaugurated the study of acoustic phonetics.
As many languages are non-phonetic -- they are not said as they look written down -- it became clear that written language could not articulate pronunciation differences. In English, for example, there are many words that are written exactly the same way but are pronounced differently such as "bow" and there are also words that are spelled differently but are said exactly the same way. Similarly, regional pronunciation differences could not be accurately recorded in a phonetic way simply by writing them in English.
The International Phonetic Alphabet is based in Latin and is a comprehensive list of every known phoneme (sound). Every documented phoneme in the world's languages is assigned its own symbol. It is used by foreign language students, speech pathologists and therapists, linguists, translators, lexicographers, singers and actors.
Each symbol in the alphabet is called a letter such as "d." Each symbol in the phonetic alphabet is called a sound segment. Each word in English is translated into phonemes and represented as sound segments. For example, the word "truth" has five letters but only four phonemes. These are represented by the four IPA phonetic symbols for the phonemes. When a word is written in its letters, it is described as orthography and when it is written phonetically it is called transcription.