Phonemes are a group of sounds used to demonstrate how two or more languages differ from one another, for example in terms of grammar. These sounds can also refer to the units of articulation that make up the sound system of a language. Sometimes, phonemes may be used as markers for dialects e.g. Southern American English features the you exchange and some African countries feature different clusters than English speakers typically do. Phoneme is usually left in lower case when referring to linguistics concepts and upper case to refer to their physical representation such as on a sound-impression device or with an IPA symbol wherever it may be used (such as in music).