From W3C Wiki
The <ruby> element allows one or more spans of phrasing content to be marked with ruby annotations.
- Ruby annotations are short runs of text presented alongside base text, primarily used in East Asian typography as a guide for pronunciation or to include other annotations.
In Japanese, this form of typography is also known as furigana.
See global attributes.
In this example, each ideograph in the Japanese text 漢字 is annotated with its reading in hiragana. [try it]:
The HTML5 specification defines the <ruby> element in 4.6.19 The ruby element.