Glottal Stop [ʔ]

The glottal stop is a voiceless plosive consonant sound, made by stopping air in the throat (glottis) as it leaves the body. In English pronunciation, the glottal stop is frequently used as an allophone of /t/ in connected speech:

Glottal Stop Usage

The glottal stop is most often heard replacing a syllable-final /t/ before another consonant sound:

notebook
wetsuit
catnap

This also occurs in connected speech where a word ends with /t/ and the next one begins with a consonant sound:

I can’t see.
What time?
Eight thirty.