Punctuation is "the use of spacing, conventional signs, and certain typographical devices as aids to the understanding and the correct reading, both silently and aloud, of handwritten and printed texts." Another description is: "The practice, action, or system of inserting points or other small marks into texts, in order to aid interpretation; division of text into sentences, clauses, etc., by means of such marks."

The colon ( : ) is a punctuation mark consisting of two equally sized dots centered on the same vertical line. A colon precedes an explanation, or an enumeration or list. A colon is also used with ratios, titles and subtitles of books, city and publisher in bibliographies, Biblical citations between chapter and verse, and—in American English—to separate hours and minutes, for business letter salutations and in formal letter writing.