Ruby characters or rubi characters are small, annotative glosses that are usually placed above or to the right of logographic characters of languages in the East Asian cultural sphere, such as Chinese hanzi, Japanese kanji, and Korean hanja, to show the logographs' pronunciation; these were formerly also used for Vietnamese chữ Hán and chữ Nôm, and may still occasionally be seen in that context when reading archaic texts. Typically called just ruby or rubi, such annotations are most commonly used as pronunciation guides for characters that are likely to be unfamiliar to the reader.

A gloss is a brief notation, especially a marginal or interlinear one, of the meaning of a word or wording in a text. It may be in the language of the text or in the reader's language if that is different.