RU

Ru is a two-letter string that appears in several coding systems and symbolic conventions across language, geography, and chemistry. In linguistics, ru is the ISO 639-1 code for the Russian language, used in language tagging and cataloging.

Geographically and electronically, RU serves as the ISO 3166-1 alpha-2 country code for Russia, and the country code top-level domain .ru is used for Russian-hosted websites and online resources. The distinction between the uppercase code RU and the lowercase domain suffix .ru reflects different standards and contexts.

In chemistry, Ru is the chemical symbol for ruthenium, a dense, silvery metal belonging to the platinum group with atomic number 44. Ruthenium is valued as a catalyst in various chemical processes and as a hardening agent in certain alloys. It also finds applications in electronics and protective coatings, including some thin-film technologies.

Beyond these primary uses, ru can appear as an abbreviation or transliteration fragment in different systems and languages. The same two letters are interpreted differently depending on case: Ru denotes the element ruthenium, while RU represents the Russia-related country code. In language tagging, the canonical form is ru (lowercase), consistent with ISO 639-1 conventions.