Espresso or caffè espresso is a concentrated coffee beverage brewed by forcing very hot, but not boiling
water under high pressure through coffee that has been ground to a consistency between extremely fine and powder.
Espresso was developed in Milan, Italy in the early 20th century, but up until the mid-1940s it was a beverage produced solely with steam pressure. The invention of the spring piston lever machine and its subsequent commercial success changed espresso into the beverage we know today.
From wikipedia