The word "ciao" (/ˈtʃaʊ/; Italian pronunciation: [1]) is an informal salutation in the Italian language that is used for both "hello" and "goodbye".

Originally from the Venetian language, it has entered the vocabulary of English and of many other languages around the world. Its dual meaning of "hello" and "goodbye" makes it similar to shalom in Hebrew, salaam in Arabic, annyeong in Korean, and aloha in Hawaiian.

The Vietnamese word chào ("hello" or "goodbye"), while similar-sounding, is unrelated in etymology.

The word derives from the Venetian phrase s-ciào vostro or s-ciào su literally meaning "I am your slave". This greeting is analogous to the medieval Latin Servus which is still used in a large section of Central/Eastern Europe. The expression was not a literal statement of fact, of course, but rather a perfunctory promise of good will among friends (along the lines of "at your service" in English). The Venetian word for "slave", s-ciào ([2]) or s-ciàvo, derives from Medieval Latin sclavus, deriving from the ethnic "Slavic", since most of the slaves came from the Balkans.

This greeting was eventually shortened to ciào, lost all its servile connotations and came to be used as an informal salutation by speakers of all classes. In modern Venetian and Lombard language, as well as in regional Lombard Italian, the word (s-ciào in Venetian, s'ciao in Lombard, ciao in Italian) is used (in addition to the meaning of salutation) as an exclamation of resignation (also in a positive sense), as in Oh, va be', ciao! ("Oh, well, never mind!"). A Milanese tongue-twister says Se gh'hinn gh'hinn; se gh'hinn nò, s'ciào ("If there is [3], there is; if there isn't, farewell! nothing we can do").