su

Su is a term that appears in many languages and contexts. As a surname, it is common in China, represented by characters such as 苏 (simplified) or 蘇 (traditional). It is also encountered as a given name or part of a name in East Asia and among diaspora communities. Notable bearers include Su Shi, also known as Su Dongpo, a Song dynasty poet.

In language coding, "su" is the ISO 639-1 code for Sundanese, a language spoken in West Java and surrounding areas. In computing, the Unix command "su" stands for substitute user or switch user, and is used to assume another user's identity, typically the superuser or root.

Historically, "SU" was the ISO 3166-1 alpha-2 code for the Soviet Union; after its dissolution in 1991 the code was retired for sovereign states. The .su top-level domain remains in existence as a legacy domain. The term Su also appears in various proper names and transliterations around the world.