A colon is a punctuation mark, with one dot above another, like this: ":".

Colons are commonly used to introduce lists, or to connect a broad idea with a specific example: two related sentences can be separated by colons instead of periods.

Table of contents
1 Examples
2 Computer representation
3 Other meanings

Examples

The United Kingdom comprises four countries: England, Wales, Scotland and Northern Ireland.
Speech is silver: silence is golden.
She hadn't eaten since breakfast: she'd worked through her lunch break.

Computer representation

In
computer programming, the colon corresponds to Unicode and ASCII character 58, or 0x003A.

Other meanings

Colon (anatomy)