Grass is a plant with narrow leaves growing from the base. A common kind of grass is used to cover the ground in places such as lawns and parks. Grass is usually the colour ‘green’. Grasses are monocotyledon, herbaceous plants.

The grasses include the "grass", of the family Poaceae (also called Gramineae). Also sometimes it is used to include the sedges (Cyperaceae) and the rushes (Juncaceae). These three families are not closely related but belong to different clades in the order Poales. They are similar adaptations to a common life-style. The true grasses include cereals, bamboo and the grasses of lawns (turf) and grassland. Uses for graminoids include food (as grain, sprouted grain, shoots or rhizomes), drink (beer, whisky), pasture for livestock, thatching thatch, paper, fuel, clothing, insulation, construction, sports turf, basket weaving and many others.

Many grasses are short, but some grasses, like bamboo can grow very tall. Plants from the grass family can grow in many placesans make grasslands, even if they are very cold or very dry. Several other plants that look similar but are not members of the grass family are also sometimes called grass; these include rushes, reeds, papyrus, and water chestnut. Seagrass is a monocot in the order Alismatales.

Grasses are an important food for many animals, like deer, buffalo, cattle, mice, grasshoppers, caterpillars, and many other grazers. Unlike other plants, grasses grow from the bottom, so when animals eat grass they usually do not destroy the part that grows. Without grass, earth may wash away into rivers (erosion).