EDIT A Colon is a punctuation mark used to introduce a list, an example or a description. It serves both as a separating and an emphasizing character.

Examples:
»He would never forget his worst birthday present: a pocket nutmeg grater.«
»The children were asked to bring the following on their first day of school: paper, a pencil, chewing gum, and an eraser.«

In Germany, the colon is often used in match scores. In Sweden, it can replace the decimal comma (3:-) and also divides book and verse in Bible references, as it does in common English usage.

History
Derived from ancient Greek (where it roughly translates as limb or phrase), the word colon originally did not signify the punctuation mark we know today but a paragraph in a verse or text. Ancient Greek texts from the 5th century BC and thus from a time when neither word spacing nor full stops at the end of a sentence existed, include vertical lines of two or three points for visual separation of sections.

See also
⋮U+22EE VERTICAL ELLIPSIS (drei Punkte)
᠁ U+1801 MONGOLIAN ELLIPSIS (vier Punkte)

Reference
Encyclopedia Britannica

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