In the botanical sense a "fruit" is the structure of a plant, usually surrounding seeds, which develops from the flower ovary after pollination and fertilization. However, popular understanding of the term is based not on plant anatomy but on usage. Thus, in a culinary sense, a fruit is the edible part of a plant which is fleshly, succulent and sweet. Its sweetness, often balanced with acid, distinguishes "fruit", in food terms, from other foods, notably vegetables. Some parts of a plant which technically are fruit are treated otherwise. Generally fruits are foods imbued with pleasure, and often eaten as the finale of a meal.
There are numerous species of fruit, from a variety of families. Many familiar fruits belong to two families in particular, Rose (Rosaceae) and Citrus (Rutaceae). Rather than botanical classification, fruits are commonly categorized by culinary characteristics: whether they have pips, stones, are berries, or soft. Fruits are also divided according to the season in which they ripen, and their place of origin.
Within species, different cultivars have been developed over the years for their individual attributes and habits.
Most fruits are suitable for eating raw, and some are well-suited to cooking. Many fruits can be preserved, often by drying, resulting in different eating and cooking properties.
Like fruit, "nut" has a botanical definition that is rather more restricted than the popular sense of the term. Botanically, nuts are fruits, specifically one-seeded fruits, with a tough, dry outer layer. In common parlance a "nut" is an edible kernel surrounded by a hard shell. Thus, fruit not technically nuts, such as almonds, and even non-fruit, such as peanuts, are treated as nuts.
Nuts generally contain little water, moderate protein, and much oil, predominantly unsaturated. Their high oil content renders nuts prone to rancidity, and to tainting by surrounding odours.
Often toasted to intensify their flavours, nuts are eaten as snacks and incorporated, whole, chopped or ground, into the sweet and savoury dishes of many cuisines.