In Swahili (the lingua franca of East Africa): someone who wanders without purpose / someone constantly on the move.
It came to be applied to all white people in East Africa, as most were encountered as traders, visiting colonial officials or tourists.
Today, white tourists are often greeted (especially by children) with the cry: "Bye bye mzungu!"
For some reason, they rarely say "Hello mzungu!" when they see one coming...
Child: "Bye bye mzungu!"
Indignant white person: "Listen, it's 'hello mzungu!' - and anyway, I've lived here for 25 years, you cheeky devil."
Child: (pause) "Bye bye mzungu!"
Ugandan Stall-holder: "A bowl of passion fruit? Um... that'll be 3,000 shillings please."
Indignant white person: "Come again? I'm not paying mzungu prices, I've lived here 25 years!" etc. etc.