The <ruby> element in HTML is used to provide pronunciation or annotation information for East Asian typography, most commonly for Chinese and Japanese text. It is especially useful for showing furigana, which are small phonetic guides placed above or alongside kanji characters to indicate their pronunciation.

A <ruby> element typically contains a base text and one or more annotations, marked using <rt> (ruby text) and optionally <rp> (ruby parentheses) elements. The <rt> element holds the pronunciation or annotation, while <rp> provides fallback text for browsers that do not support ruby annotations.

For example, in Japanese, the kanji 漢 might be annotated with the furigana かん (kan) to help readers pronounce it correctly. When rendered, the base character appears normally, and the annotation appears in a smaller font above or to the side.

The <ruby> element is semantically meaningful: it signals that the enclosed text has an associated pronunciation or explanatory note, which can aid readers, accessibility tools, and text-to-speech systems. Beyond Japanese and Chinese, <ruby> can also be used in educational contexts or for providing transliterations, pronunciation guides, or glosses for any text that may require additional clarification.