As the avocado's Latin name confirms, Persea americana, it is a native of the New World. It has long been in important ingredient in native diets in Mexico, Central & South American and the Caribbean. The word avocado, derives from the Nahuatl ("Aztec") word ahuacatl, which roughly translates as "green testicle," in reference to the show of the fruit. It was because of this that the fruit was considered an important symbol of fertility in Mexico, a practice that may be really ancient in the area, since the oldest evidence of them was found in a cave in Puebla that dates to about 10,000BC!
Although they are known principally as a "fruit" that is used in salads or, more often, made in the Guacamole (Nahuatl Ahuacatl Molli), they are actually quite versatile and have all kinds of uses around the world. In India they are known as "the Butter Fruit" and are used like butter. In Britain, Avocado Ice Cream can be found. In China they are some times eaten with soy sauce or soy based dressings. In Japan (by way of the US) they put in sushi rolls, and are a very important part of the "California Roll." In the Middle East they are mixed with Tahini and served as a dip for Arabic Breads.
In native preparations, there are many different way of serving avocados. In addition to Guacamole, in Mexico they are used as a ubiquitous garnish on anything from Tortilla Soup, to tostadas, Huevos Rancheros, tacos, enchiladas, and the like. In Brazil that turn them into a sweet, Avocado Cream. In Venezuela, they are chopped into a native sauce and served Arepas. In the Caribbean they put into soups, stuffed and made into mayonnaise. In the southern United States they are often pickled in vinegar or dressed with Native dressing "on the half shell." There is a Florida avocado, which I was all I knew until my late teens, when Hass avocados arrived in local supermarkets. It is bigger, less fatty and perfect for pickling or putting into green salads.
They can be put into pies (in south Florida there a version of Key Lime Pie that uses them), made into quick breads, made into muffins, made into sweet icing, put on crostini, put into sandwiches, made into smoothies...you name it!