Exclamation point
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An exclamation point refers to the ! symbol. It is used for emphasis, although in formal writing, its use is generally limited. In mathematics, the exclamation point means "factorial", and can be placed after integers to indicate the multiplication of that integer by all preceding positive integers . For instance, 5! can be read as "5 factorial", which means "5 times 4 times 3 times 2 times 1". 0! is defined to be 1.
The upside down version is ¡