Long is an English equivalent of 'lungo'. It's a masculine adjective that's pronounced 'LOON-goh'. It's used to describe a certain kind of espresso coffee, in which there's twice the usual amount of water. Running twice the amount of water results in a longer pull/fill time. It thereby results in a greater amount of time for the water to pass through the coffee grounds. The longer pull/fill time therefore adds extracts that don't dissolve in the regular amount of time. The resulting espresso reflects the slower passage and the greater contribution of extracts to the taste. That's what accounts for the lungo's weaker, but more bitter taste.
In addition a “long” pull (extraction) of espresso made with the same amount of finely ground coffee and twice the water of a normal shot. A single serving is about 2 ounces.
It may sound similar to a Caffé Americano, but its unique processing results in a different flavor. It has a less strong taste (because it is made with more water), but it also has more bitterness (because the extraction process takes longer and pulls more bitterness out of the grounds).
