The avocado is a tree and the fruit of that tree, Persea americana, in the flowering plant Family Lauraceae. The avocado tree does not tolerate freezing temperatures, and so can be grown only in subtropical and tropical climates, where the fruit is sometimes called a pear or alligator pear.
Avocado fruit is a berry. Horticultural varieties range from more or less round to egg or pear-shaped, typically the size of a temperate zone pear or larger, on the outside bright green to green-brown (or almost black) in color, and high in fat, with a large central seed or pit. The flesh is typically greenish yellow to golden yellow, if ripe turning dark soon after exposure to air. The avocado is very popular in vegetarian cuisine, making a good substitute for meats and cheeses in sandwiches because of the high fat content. The fruit is not sweet, but starchy, flavorful, and of smooth, almost creamy texture. It is used as the base for the Mexican sauce known as guacamole (simply an abbreviation of aquacate mole, or "avocado sauce" in Spanish).
The avocado fruit does not ripen on the tree - once mature, the fruit must be picked, and will then ripen in a few days, faster if stored with other fruit such as bananas. Fruit can be left on the tree until required, rather than picked and stored.