Strikethrough (also called strikeout) is a typographical presentation of words with a horizontal line through their center.
This is an example.
It signifies one of two meanings. In ink-written, typewritten, or other non-erasable text, the words are a mistake and not meant for inclusion. When used on a computer screen, however, it indicates recently deleted information. It can also be used deliberately to imply a change of thought; for example: "John Doe is
an idiot not very intelligent."
Computer representations 
BB Code 
The BB Code for strikethrough is
In cascading style sheets (CSS) strikethrough is controlled using the
text-decoration property, and specified by the
line-through value of that property. For example,
<span style="text-decoration: line-through;">ABCD efghi</span> renders like this: ABCD efghi
Combining characters 
The “combining long stroke overlay” (U+0336) results in an unbroken stroke across the text:
- Combined: A̶B̶C̶D̶ ̶e̶f̶g̶h̶i̶
while the “combining short stroke overlay” (U+0335) results in individually struck out characters:
- Combined: A̵B̵C̵D̵ ̵e̵f̵g̵h̵i̵
Similarly, the “combining short solidus overlay” (U+0337) results in diagonally struck out letters:
- Combined: A̷B̷C̷D̷ ̷e̷f̷g̷h̷i̷
as does the “combining long solidus overlay” (U+0338), which produces longer diagonal strokes:
- Combined: A̸B̸C̸D̸ ̸e̸f̸g̸h̸i̸
Specific struck-through characters 
A number of characters that have the visual appearance of struck-through characters exist in Unicode, including ƀ, Đđ, Ǥǥ, Ħħ, Ɨɨ, Ɉɉ, Łł, Ɵɵ, Ŧ, ʉ, Ƶƶ, ƻ, ʡ, ʢ, Ғғ, Ҟҟ, Ұұ, Ҍҍ. These usually have specific functions (for example, in the Latin Extended-A character set) or representations and are not intended for general use. However, they are not precomposed characters and have neither canonical nor compatibility decompositions. This issue has created security considerations since "precomposed" characters like U+019F and sequences like U+004F U+0335 or U+004F U+0336 often cause visual confusion (compare Ɵ and O̵ and O̶). Unicode has acknowledged this issue and has proposed a standardized method for counteraction
Historical uses 
Double/multiple strikethrough 
Double strikethrough is an option in certain word processing applications such as Microsoft Word. There is no generally agreed meaning of double strikethrough, but it may be used as a second level of single strikethrough.
In Japan, double strikethrough is conventionally used (rather than single strikethrough) when striking out text. This is for added clarity, as in complex kanji a single strikethrough may be missed or confused with a stroke in the character.
Double, triple or multiple strikethrough may also (especially formerly) be used as a way of emphasising words. In this function it is likely to be misunderstood by the reader.
See also 
- W3C HTML 4 Specification: Presentation
- W3C HTML 4 Specification: Paragraphs, Lines, and Phrases
- The Unicode Consortium, The Unicode Standard, Chapter 2, Page 44, Non-decomposition of Overlaid Diacritics
- The Unicode Consortium, Unicode Technical Standard #39: Unicode Security Mechanisms, chapter Confusable Detection