The term cha-cha comes from Haiti, where it referred to a component of a bell which made a "cha-cha" noise when it was rubbed. The device was kept and used as an instrument.
The music of cha-cha-cha, however, evolved from mambo. In the late 1940s, mambo was wildly popular across the United States, but it was very fast and difficult to dance to. Orchestras slowed down the mambo, and cha-cha-cha was the result. In 1951, Cuban composer and violinist Enrique Jorr n introduced the cha-cha-cha rhythms under this name to Cuban dance floors while playing with Orquestra America. Some say that he came to this idea as early as in 1948 while being with Antonio Arca o's orchestra. In 1953, his "La Enga adora" and "Silver Star" became recorded hits. The dance teacher Pierre Lavelle from the United Kingdom, a founder of the Latin American Faculty of the ISTD, visited Cuba in 1952 to discover mambo (some say, rumba) danced with the triple step in place of the slow one. He brought this dance idea to the Europe and eventually created what is known now as ballroom Cha-cha-cha.
In early days, this dance and its music were both known as "triple mambo" or "mambo with guiro rhythm".
ChaChaCha is a long wait, but certainly worth it for the unique ambience and great tapas (a series of appetizers that you eat as a meal).
When I first went to ChaChaCha a few years back, I was a bit overwhelmed by the immense crowd and noise inside; it's almost like being in a subway car, and it takes some amount of balance to walk around without spilling the potent sangria on an unsuspecting patron.
ChaChaCha is _the_ tapas restaurant for me, and a great place to go out and spend a festive (and leisurely) evening with friends or a loved one.