Avocado comes from the Nahuatl word ahuacatl, which means testicle. It has nothing to do with the Spanish word abogado, which means lawyer, because in southern Mexico and Guatemala, where the plant originates, they call it aguacate. With the trade going on in the Americas for hundreds (thousands?) of years before Columbus arrived, it's not surprising that the tree made its way to South America, where its fruit is called palta.
Yes, Persea americana is a fruit, not a vegetable, in spite of its USDA classification. Spanish friars introduced the tropical avocado tree into sub-tropical Southern California, and today San Diego County produces 95% of the nation's avocados. Early Yankees who settled here called the strange fruit "alligator pear" but you won't hear that term used much anymore, although it appears in history books and old recipes.
Avocados have had a bad reputation for a number of years, because they were known to be high in fat. During the fat-phobic '80's and well into the 90's, nutritionists, physicians, and the American Heart Association urged limiting the consumption of avocados due to concerns about its effect on cholesterol. (These are the same people who told us to eat imitation eggs.) The result was that many people got the impression that avocados were high in cholesterol, which is impossible, since cholesterol is a fatty substance produced by the livers in animals, not plants. What avocados do contain is monounsaturated fat, which has since been found to be beneficial. It's also packed with lots of other nutrients, such as folates, antioxidants, more potassium than a banana, protein, and fiber. We would do well to eat more avocados.
Which is the problem. The worldwide consumption of avocados has skyrocketed, which is great for the avocado producers but hard on us who used to buy four for a dollar (no more). And commercially prepared guacamole is grabbing an ever larger chunk of production. The problem is that not many places grow avocados. Europeans, whose only encounter with the fruit might be during a cruise to Yucatán, are now adding it to their salads, even though the closest avocado grove to Europe might be in Algeria. For a long time, only Mexico, California, and Florida produced export quantities, but now Chile, Australia, and New Zealand are getting into the market. But don't look for prices to fall soon.
There are many varieties of avocado, but the one you're most likely to find in your supermarket is the Hass (frequently mispronounced -- and misspelled -- "Haas"). This is the producer's favorite, because it ships well. Its thick skin protects it from bruising and mishandling. But the Hass, whose skin turns black when fully ripe, was initially not well accepted by American housewives, who preferred the smooth, green skin of the larger Fuerte. But effective marketing eventually warmed the consumer to the Hass, while there remain many avocado lovers (particularly in Florida and Mexico) who still seek out other varieties, such as Fuerte, Bacon, and Reed. (Mexican guacamole is usually made with Reed avocados.)
Most people think of guacamole as the primary use for the avocado. However, avocado slices go well on any salad and in most sandwiches. In Chile, it is standard to serve plain mashed avocado, seasoned only with a little salt, as a spread on bread or toast for breakfast or tea.