The ditto mark (″) is a typographic symbol indicating that the word(s) or figure(s) above it are to be repeated. For example:
Black pens, box of twenty
Blue ″ ″ ″ ″
The word ditto comes from the Tuscan language, where it is the past participle of the verb dire (to say), with the meaning of “said”, as in the location “the said story”. The first recorded use of ditto with this meaning in English occurs in 1625. Early evidence of ditto marks can be seen on a cuneiform tablet of the Neo-Assyrian period (934 – 608 BC) where two vertical marks are used in a table of synonyms to repeat text, while in China the corresponding mark is two horizontal lines (二); see iteration mark.
An advertisement from 1833. The second item on the list can be read as "Prime American Pork, in barrels", while the third is "Prime American Pork, in Half barrels".
For Western scripts, including Latin script, Unicode has not defined a separate ditto character, but instead U+2033″double prime (HTML: ″″) may be used for this purpose. In practice, however, closing double quotation marks (”) or straight double quotation marks (") are often used instead. The abbreviation do. is also used. [see above]
For East Asian scripts (CJK, specifically Bopomofo, Hangul, Han, Hiragana and Katakana), the full-width ditto mark is U+3003〃ditto mark (HTML: 〃 block: CJK Symbols and Punctuation)