A crop is a volunteered or cultivated plant (any plant) whose product is harvested by a human at some point of its growth stage. Plants which have not been cultivated but whose product are harvested, are not really classified as crops. The same goes for plants which have been planted, but are never harvested. Flowers are classified as crops because when it has been cultivated, its harvesting also include the aesthetic purpose it serves. Crops refer to plants of same kind that are grown on a large scale for food, clothing, and other human uses. They are non-animal species or varieties grown to be harvested as food, livestock fodder, fuel or for any other economic purpose (for example, for use as dyes, medicinal, and cosmetic use).

Major crops include sugarcane, pumpkin, maize (corn), wheat, rice, cassava, soybeans, hay, potatoes and cotton.

Source: Wikipedia