hollayoudaoicibaDictYouDict[holla 词源字典]
as a command to "stop, cease," 1520s, from French holà (15c.). As a command to get attention, from 1580s. As an urban slang form of holler (v.) and meaning "greet, shout out to," it was in use by 2003.[holla etymology, holla origin, 英语词源]