Uncontacted Tribes

Wow, what exactly does it mean to be uncontacted tribe? Does it mean that they've never seen anyone other than the people in their tribe? What do they think of the helicopters and airplanes flying over their heads? Do they have any comprehension of the size of the world and the technology in a modern city? What would it be like for one of them to be plopped down in the middle of Manhattan or Tokyo?