The hamzah (الهَمْزة‎) is the Arabic letter specifically designated as the glottal stop. Because of its later arrival in the alphabet, it is not considered to be one of the 28 "full" letters.

A glottal stop is a short pause of sound produced by obstructing airflow while speaking. In English, this is used in the words uh-oh and hawai'i.

Historically ا (alif) (ا) served as the glottal stop, but through time because more associated with the a sound. For the sake of clarity, the hamzah was added. Its shaped is based on the letter ع (ᶜayn) (ع), which also produces a sound not found in English.

The hamzah can be written alone or as a diacritical above alif, waaw, and and yaa'.