In this post that I ran across online written by an American discovering the pleasures of coffee in Auckland, New Zealand, the writer mentioned how she was a little lost because of the different coffee terminology used in New Zealand, and one of the coffee drinks she referred to while scratching her head was a "long black". It seems that by the end of her visit she still didn't know quite what the heck a long black was, so let me answer the question for her and anyone else out there in cyberspace.
A long black is a double-shot of espresso pulled over hot water. Take note: the espresso is pulled into the hot water so as not to break the crema; there should be crema floating on the top of a long black.
As a matter of convenience, the hot water is typically taken from the espresso machine itself rather than from a separate hot water source. In a way, a long black is similar to an Americano, but Americano is typically a single shot of espresso with more hot water, and it is likely in the U.S. that the espresso will be extracted separately into a small pitcher and the espresso then poured into the hot water. Oh what a shame; crema down the drain!
Long black's partner is the "short black" coffee which is simply the traditional shot of espresso coffee served in a demitasse cup.
Espresso Coffee Snobs