The glottal stop is a type of consonantal sound used in many spoken languages, produced by obstructing airflow in the vocal tract or, more precisely, the glottis. The symbol in the International Phonetic Alphabet that represents this sound is ⟨ʔ⟩. Using IPA, this sound is known as a glottal plosive.
In English, the (phonemic) glottal stop occurs as an open juncture (for example, between the vowel sounds in uh-oh!) and allophonically in T-glottalization. For most US English speakers, a glottal stop is used as an allophone of /t/ between a vowel and "m" (as in atmosphere or Batman) or a syllabic "n" (as in button or mountain) except in slow speech. In British English, the glottal stop is most familiar in the Cockney pronunciation of "butter" as "bu'er". Additionally, there is the glottal stop as a null onset for English, in other words, it is the non-phonemic glottal stop occurring before isolated or initial vowels (for example, representing uh-oh!, [ˈʌʔoʊ] and [ˈʔʌʔoʊ] are phonemically identical to /ˈʌ.oʊ/).
Features of the glottal stop:
Its manner of articulation is occlusive, which means it is produced by obstructing airflow in the vocal tract. Since the consonant is also oral, with no nasal outlet, the airflow is blocked entirely, and the consonant is a stop.
Its phonation is voiceless, which means it is produced without vibration of the vocal cords; necessarily so, because the vocal cords are held tightly together, preventing vibration.
It is an oral consonant, which means air is allowed to escape through the mouth only.
Because the sound is not produced with airflow over the tongue, the central–lateral dichotomy does not apply.
The airstream mechanism is pulmonic, which means it is articulated by pushing air solely with the lungs and diaphragm, as in most sounds.