Cucumis sativus, is a widely cultivated plant in the gourd family Cucurbitaceae, which includes squash, and in the same genus as the muskmelon.

The cucumber is a creeping vine that roots in the ground and grows up trellises or other supporting frames, wrapping around ribbing with thin, spiraling tendrils. The plant has large leaves that form a canopy over the fruit.

The fruit is roughly cylindrical, elongated, with tapered ends, and may be as large as 60 cm long and 10 cm in diameter. Cucumbers grown to be eaten fresh (called slicers) and those intended for pickling (called picklers) are similar. Cucumbers are mainly eaten in the unripe green form. The ripe yellow form normally becomes too bitter and sour.

Having an enclosed seed and developing from a flower, cucumbers are scientifically classified as fruits. Much like tomatoes and squash, however, their sour-bitter flavor contributes to cucumbers being perceived, prepared and eaten as vegetables, which is the accepted culinary term.

A few varieties of cucumber are parthenocarpic, the blossoms creating seedless fruit without pollination. Pollination for these varieties degrades the quality. In the US, these are usually grown in greenhouses, where bees are excluded. In Europe, they are grown outdoors in some regions, and bees are excluded from these areas. Most cucumber varieties, however, are seeded and require pollination. Thousands of hives of honey bees are annually carried to cucumber fields just before bloom for this purpose. Cucumbers may also be pollinated by bumblebees and several other bee species.

Symptoms of inadequate pollination include fruit abortion and misshapen fruit. Partially pollinated flowers may develop fruit which are green and develop normally near the stem end, but pale yellow and withered at the blossom end.

Traditional varieties produce male blossoms first, then female, in about equivalent numbers. New gynoecious hybrid cultivars produce almost all female blossoms. However, since these varieties do not provide pollen, they must have interplanted a pollenizer variety and the number of beehives per unit area is increased. Insecticide applications for insect pests must be done very carefully to avoid killing off the insect pollinators.

Cucumbers originated in India. Therefore, the English word cucumber is derived from Indian word "kachumbar". Large genetic variety of cucumber has been observed in different parts of India. It has been cultivated for at least 3,000 years in Western Asia, and was probably introduced to other parts of Europe by the Romans. Records of cucumber cultivation appear in France in the 9th century, England in the 14th century, and in North America by the mid-16th century.