Notation
Phonemes are conventionally placed between slashes in transcription, whereas speech sounds (phones) are placed between square brackets. Thus /pʊʃ/ represents a sequence of three phonemes /p/, /ʊ/, /ʃ/ (the word push in standard English), while represents the phonetic sequence of sounds (aspirated "p"), (the usual pronunciation of push).
(Another similar convention is the use of angle brackets to enclose the units of orthography, namely graphemes; for example, ⟨f⟩ represents the written letter (grapheme) f.)
The symbols used for particular phonemes are often taken from the International Phonetic Alphabet (IPA), the same set of symbols that are most commonly used for phones. (For computer typing purposes, systems such as X-SAMPA and Kirshenbaum exist to represent IPA symbols in plain text.) However descriptions of particular languages may use different conventional symbols to represent the phonemes of those languages. For languages whose writing systems employ the phonemic principle, ordinary letters may be used to denote phonemes, although this approach is often hampered by the complexity of the relationship between orthography and pronunciation (see Correspondence between letters and phonemes below).
Read more about this topic: Phoneme