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.
The name"avocado" is from its Nahuatl name 'ahuacatl' which also meant testicles, with influence from the irrelevant but much more familiar Spanish avocado an obsolete form of 'abogado' (lawyer). The Nahuatl ahuacatl could be compounded with others, as in ahuacamolli, meaning “avocado soup or sauce,” from which the Spanish-Mexican word guacamole derives.
The avocado fruit does not ripen on the tree, but will fall off in a hard, "green" state, then ripen quickly on the ground. Generally, the fruit is picked once it reaches a mature size, and will then ripen in a few days — faster if stored with other fruit such as bananas. Up to a point, fruit can be left on the tree until required, rather than picked and stored.
Avocados have a taste reminiscent of Thousand-year Eggs.
Barlow & Martin (2002) identify the avocado as a fruit adapted for ecological relationship with large mammals, now extinct (as for example the South American herbivorous giant ground sloths or Gomphotheres). This fruit with its mildly toxic pit, co-evolved with those extinct mammals to be swallowed whole and excreted in dung, ready to sprout. The ecological partners have disappeared, and the avocado plant has not had time to evolve an alternative seed dispersal technique.