It's a common greeting used in Latin America, especially in Argentina and Uruguay, where it's often used as a more informal way to say goodbye than "adiós".
However, "Ariba" is also the name of a well-known software company, Ariba, Inc. which specializes in business-to-business (B2B) commerce and supply chain management solutions. So, the meaning of "Ariba" depends on the context in which it is used.