Calamari is the Italian word for squid (singular: calamaro), and recipes for fried calamari are found in a number of Mediterranean cuisines.
Calamari is usually made from the European squid, which is plentiful in the Mediterranean as well as the Adriatic sea, the North Sea, Irish Sea, and the Eastern parts of the Atlantic Ocean from as far north as the British Isles to the coasts off of equatorial Africa.
Similar species can be found along the east coast of the United States, and also along the California coast. Full grown squid can be anywhere from 12 to 24 inches long.
Fried calamari is usually served as an appetizer, garnished with lemon and parsley and served with some sort of dipping sauce. Typical sauces for calamari include marinara sauce, flavored mayonnaise or aioli, tartar sauce or yogurt.
In addition to frying, calamari can also be sauteed, grilled, boiled or braised.
The trick with calamari is to either cook it very quickly (i.e. not more than three minutes), or for a very long time, (i.e. three hours or longer). Anything in between and the calamari can turn out very tough and rubbery. For example, it can be simmered in a tomato sauce until tender and then served with pasta.
To prepare calamari, the squid has to be cleaned. This involves removing the head, viscera and inner cartilage (called the quill), something called the beak, along with the fins and skin.
The tentacles and body are the edible portions.
Here's a video that shows how to clean a squid.
Usually, the squid body is sliced crosswise, which yields the characteristic calamari rings that are then prepared as described above. But the body can also be split and flattened out to produce what's called a calamari steak.
It's a good idea to score the steak in a diamond pattern to help keep it flat. And of course, cook it quickly over high heat. Deep-frying accomplishes this perfectly, which is why it's one of the most common ways of preparing calamari.
It's a good idea to use a light, thin batter when frying calamari. If the batter is too thick, or if it's been overmixed or even if the liquid in the batter is too warm, the coating can turn out heavy and bready rather than light and crispy.