H-dropping or aitch-dropping is the deletion of the voiceless glottal fricative or "H-sound", [h]. The phenomenon is common in many dialects of English, and is also found in certain other languages, either as a purely historical development or as a contemporary difference between dialects. Although common in most regions of England and in some other English-speaking countries, and linguistically speaking a neutral evolution in languages, H-dropping is often stigmatized as a sign of careless or uneducated speech.
The reverse phenomenon, H-insertion or H-adding, is found in certain situations, sometimes as an allophone or hypercorrection by H-dropping speakers, and sometimes as a spelling pronunciation or out of perceived etymological correctness. A particular example of this is the spread of 'haitch' for 'aitch'.
In Old English phonology, the sounds [h], [x], and [ç] (described respectively as glottal, velar and palatal voiceless fricatives) are taken to be allophones of a single phoneme /h/. The [h] sound appeared at the start of a syllable, either alone or in a cluster with another consonant. The other two sounds were used in the syllable coda ([x] after back vowels and [ç] after front vowels).
The instances of /h/ in coda position were lost during the Middle English and Early Modern English periods, although they are still reflected in the spelling of words such as taught (now pronounced like taut) and weight (now pronounced in most accents like wait). Most of the initial clusters involving /h/ also disappeared (see H-cluster reductions). As a result, in the standard varieties of Modern English, the only position in which /h/ can occur is at the start of a syllable, either alone (as in hat, house, behind, etc.), in the cluster /hj/ (as in huge), or (for a minority of speakers) in the cluster /hw/ (as in whine if pronounced differently from wine). The usual realizations of the latter two clusters are [ç] and [ʍ] (see English phonology).