Most people probably mean both taste and caffeine, but generally, it's more about the taste. And that stronger taste can be achieved in a couple of ways, most usually either with darker roasted beans or more coffee in the coffee/water ratio than "normal."
Similarly one may ask, which country is the largest coffee producer in the world today?
Brazil - 2,595,000 metric ton (5,714,381,000 pounds) Brazil is the world's largest coffee producer. In 2016, Brazil produced a staggering 2,595,000 metric tons of coffee beans. It is not a new development, as Brazil has been the highest global producer of coffee beans for over 150 years.
How does the grind affect the taste of coffee?
In general, if you brew coffee that is ground too coarse, the coffee can be under-extracted (weak), and less flavorful. If your coffee is ground too fine, however, the coffee can be over-extracted and bitter. Small changes in grind size can drastically affect the taste of your final brew.
What is a weak coffee?
Some people mistakenly refer to a dark roast as a 'strong' coffee. While certainly there are some coffees with stronger flavors than others, the actual meaning of STRONG coffee refers to a high ratio of coffee grounds to water. Conversely, 'Weak' coffee is coffee that is brewed with a lower coffee to water ratio.