In phonetics, aspiration is the strong burst of air that accompanies either the release or, in the case of preaspiration, the closure of some obstruents. To feel or see the difference between aspirated and unaspirated sounds, one can put a hand or a lit candle in front of one's mouth, and say pin and then bin . One should either feel a puff of air or see a flicker of the candle flame with pin that one does not get with bin. In most dialects of English, the initial consonant is aspirated in pin and unaspirated in bin.
The diacritic for aspiration in the International Phonetic Alphabet (IPA) is a superscript "h", ⟨◌ʰ⟩. In Unicode, it is encoded at U+02B0 ʰ modifier letter small h (HTML:
ʰ). Unaspirated consonants are not normally marked explicitly, but there is a diacritic for non-aspiration in the Extensions to the IPA, the superscript equal sign, ⟨◌⁼⟩.
The term "aspiration" is sometimes also used for the replacement of a (usually fricative) consonant with an sound, but that process is more accurately termed debuccalization.