The actual sound produced, such as a simple vowel or consonant sound is called phone.
Closely associated with Phonetics is another branch of Linguistics known as Phonology. Phonology deals with the way speech sounds behave in particular languages or in languages generally. This focuses on the way languages use differences between sounds in order to convey differences of meaning between words. All theories of phonology hold that spoken language can be broken down into a string of sound units (phonemes). A phoneme is the smallest ‘distinctive unit sound’ of a language. It distinguishes one word from another in a given language. This means changing a phoneme in a word, produces another word, that has a different meaning. In the pair of words (minimal pairs) ‘cat’ and ‘bat’, the distinguishing sounds /c/ and /b/ are both phonemes. The phoneme is an abstract term (a speech sound as it exists in the mind of the speaker) and it is specific to a particular language.
A phoneme may have several allophones, related sounds that are distinct but do not change the meaning of a word when they are interchanged. The sounds corresponding to the letter “t” in the English words ‘tea’ and ‘trip’ are not in fact quite the same. The position of the tongue is slightly different, which causes a difference in sound detectable by an instrument such as a speech spectrograph. Thus the [t] in ‘tea’ and the [t] in ‘trip’ are allophones of the phoneme /t/.
Phonology is the link between Phonetics and the rest of Linguistics. Only by studying both the phonetics and the phonology of English is it possible to acquire a full understanding of the use of sounds in English speech.