The official English-language typography term for what is known in Japanese as furigana. Ruby text describes text which appears in a small font above the base text. Optionally, a third line of text can also be made to appear beneath the baseline.
The World Wide Web Consortium has established a recommendation to include ruby text on the web (more info: http://www.w3.org/TR/1998/WD-ruby-19981221/) but it is not yet part of the XHTML specification. Many desktop publishing and word processing programs support ruby text, including Microsoft Word 2000 and higher with support for Asian languages installed.