What is "preaspiration"

n. (context phonetics English) a period of voiceless breathing that precedes some consonants in some languages -- a sort of mirror-image of aspiration

In phonetics, preaspiration (sometimes spelled pre-aspiration) is a period of voicelessness or aspiration preceding the closure of a voiceless obstruent, basically equivalent to an -like sound preceding the obstruent. In other words, when an obstruent is preaspirated, the glottis is opened for some time before the obstruent closure. To mark preaspiration using the International Phonetic Alphabet, the diacritic for regular aspiration, , can be placed before the preaspirated consonant. However, prefer to use a simple cluster notation, e.g. instead of .