What is the meaning of ǃ?

the forward release of an alveolar click.

the tenuis velar or sometimes uvular alveolar click, [k͜ǃ] or [q͜ǃ]

[ǃ]-coloring or a weak, fleeting or epenthetic [ǃ]-release.

A letter of the Juǀ'hoan alphabet, written in the Latin script.

A letter of the Khoekhoe alphabet, written in the Latin script.

Source: wiktionary.org