What is an Espresso Machine?

There are many types of espresso machines, below is a commonly used machine and is the type referred to throughout this webpage:

Figure 2: The Astoria Argenta pump, semi-automatic machine.

This is called the Astoria Argenta SAE2. This machine has two sides and is powered by a pump. The classification of the Astoria Argenta SAE2 is a semi-automatic, pump operated espresso machine. The next few links will make this a much clearer.