Espresso Lungo is an extended pour, double the water through the same amount of ground coffee. Ideally, the coffee should be ground more course than usual espresso grounds, so that twice as much water will pass through the coffee in the same amount of time. The result is a very bitter, slightly weaker espresso shot.
Many connoisseurs consider Espresso Lungo to be overextracted. Although it is some people's cup of tea, (coffee?).
At many coffeehouses in North America, Espresso Lungo is passed off as plain old Espresso. A demitasse holds two ounces to accommodate Espresso Lungo, or just a double Espresso. But so many improperly trained baristas fill the mug thinking it's a normal shot.