"Ciao," meaning "goodbye," is fairly common in the United States but it carries a sense of sophistication--as if you were someone rich who traveled to Europe at a lot. "Chau" must be common in Latin America because some of my Spanish language partners use it. ahdictionary.org includes it as a legitimate U.S. English word, and notes that "The Italian salutation ciao, which is now popular in many parts of the world outside Italy." It says that it "originated in the dialects of northern Italy. In the dialect of Venice, ciau literally means 'servant, slave,' and is also used as a casual greeting, 'I am your servant.'"

As the previous users said "Ciao" is an italian word that means both Hi and Goodbye and it's common to say in Italy "Ciao ciao" if you want to say goodbye in an informal way and also to close a conversation at the phone with a person that you know very well. I'm a little bit surprised that other countries has adopted this word as a greeting

Hi Claire, In addition to what Ritsumei and Hana said, Chao is used by the Vietnamese as well. Spelled slightly different, but pronounced the same aside from tonal accent differences. Chao is Hi,, Xin Chao is Hello.

I've heard people use it. It's Italian for hi/goodbye (pronounced Ch" as in Channel and "Ou" as in "owl") - some English speakers have adopted it for saying hello and goodbye, how often you hear it depends on where you are.

Chao is a loan word from Italian. In Italian, I think it can mean both hello and goodbye, but I have mostly heard it used for goodbye. In my area of America, it isn't very common, but it would probably still be understood.