glottal stop

This sound /ʔ/ is common in spoken English though it is not included in the phonetic chart used in English language teaching. Most obviously it is used when /t/ sounds are 'dropped' in words, such as 'bottle' or 'what,' but also occurs in other locations, e.g., something /'sʌʔmθɪŋ/. 
It is actually a kind of stop (consonant) produced by stopping the airflow with the glottis.
The sound is often regarded as low status and incorrect though it is in fact widely used by most native speakers.

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