Colon (punctuation)

The colon (":") is a punctuation mark, simply consisting of two equally sized and vertically aligned dots.
Punctuation
Use in prose
A colon is a more significant pause than a semicolon. It is usually used to contrast two parts of a sentence:
It's official: McClaren makes the worst start by an England manager.
When the door was forced, a scene of chaos was revealed: chairs overturned, drawers puu66tw7rz3,dlled out and emptied, broken crockery on the floor...
If you must go, take the following: climbing rope, ice axe, compass, a large-scale map, water and food, and good boots.
Man proposes: God disposes.
The Lord seeth not as man seeth: for man looketh on the outward appearance, but the Lord looketh on the heart.
Use in other kinds of text
Introduction of a definition, such as:
A: the first letter in the Latin alphabet
Hypernym of a word: a word having a wider meaning than the given one; e.g. vehicle is a hypernym of car
Separation of the chapter and the verse number(s) indication in many references to religious scriptures, and also epic poems; it was also used for chapter numbers in roman numerals, as in:
John 3:14-16 (or John iii:14-16) (cf. chapters and verses of the Bible)
The Qur'an, Sura 5:18
Separation when reporting time of day hour/minute/second (cf. ISO 8601), such as:
The concert finished at 23:45.
This file was last modified today at 11:15:05.
Separation of a title and the corresponding subtitle, as in:
Star Wars Episode IV: A New Hope
Separation of clauses in a periodic sentence
Colons can also be used to start a list, such as, "He provided all of the ingredients: sugar, flour, eggs, and butter."
History
The colon's first appearance in English text is marked by the Shorter Oxford English Dictionary as 1589.
Diacritical usage
A special double-triangle colon symbol is used in IPA to indicate that the preceding sound is long. Its form is that of two triangles, each a bit larger than a point of a standard colon, pointing toward each other. It is available in Unicode as modifier letter triangular colon, Unicode U+02D0 (). A regular colon is often used as a fallback when this character is not available, or in the practical orthography of some languages (particularly in Mexico), which have a phonemic long/short distinction in vowels.
Mathematics
The colon is also used in mathematics, cartography, model building and other fields to denote a ratio or a scale, as in 3:1 (pronounced "three to one"). A betting odd of the form corresponds to the probability . Unicode provides a distinct ratio character, Unicode U+2236 () for mathematical usage.
In many non-English-speaking countries, the colon is used as a division sign: "a divided by b" is written as a : b.
The combination with an equal sign, , is used for definitions.
Computing
In computing, the colon character is represented by ASCII code 58, and is located at Unicode code-point U+003A. The full-width (double-byte) equivalent, :, is located at Unicode code point U+FF1A.
The colon is quite often used as a special control character in many operating systems commands, URLs, computer programming languages, and in the path representation of several file systems. It is often used as a single post-fix delimiter, signifying the immediate precedence of a token keyword or the transition from one mode of character string interpretation to another related mode. Some applications, such as the widely used MediaWiki, use the colon as both a pre-fix and post-fix delimiter.
For a double-colon, "::" the meaning has included the use of ellipsis, as spanning over omitted text; however, there have been other meanings as well.
Internet usage
On the Internet (online chats, email, message boards, etc.), a colon or multiple colons is sometimes used to denote an action or emote. In this use, it has the inverse function of quotation marks--denoting actions where unmarked text is assumed to be dialog. For example:
Kim: Pluto is so small, it should not be considered a planet. It is tiny!
Mel: Oh really? ::Drops Pluto on Kim's head:: Still think it's small now?
Colons may also be used for sounds (as with ":Click:"). One can contrast this use with the use of outer asterisks (for example, *cough* would denote that the speaker is coughing, as opposed to saying the word 'cough').