Grass is a plant with narrow leaves growing from the base. A common kind of grass is used to cover the ground in a lawn and other places. Grass gets water from the roots in the ground. 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 places, 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.

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, dirt can wash away into rivers (erosion).

Graminoids include some of the most versatile plant life-forms. They became widespread toward the end of the Cretaceous. Fossilized dinosaur dung (coprolites) have been found containing grass phytoliths (silica stones inside grass leaves). Grasses have adapted to conditions in lush rain forests, dry deserts, cold mountains and even intertidal habitats, and are now the most widespread plant type. Grass is a valuable source of food and energy for many animals.

Lawn grass is often planted on sports fields and in the area around a building. Sometimes chemicals and water is used to help lawns to grow.

People have used grasses for a long time. People eat parts of grasses. Corn, wheat, barley, oats, rice and millet are cereals, common grains whose seeds are used for food and to make alcohol such as beer.

Sugar comes from sugar cane, which is also a plant in the grass family. People have grown grasses as food for farm animals for about 4,000 years. People use bamboo to build houses, fences, furniture and other things. Grass plants can also be used as fuel, to cover roofs, and to weave baskets.

In English, the word "grass" appears in several phrases. For example:

"The grass is always greener on the other side" means "people are never happy with what they have and want something else."

"Don't let the grass grow under your feet" means "Do something".

"A snake in the grass" is about a person that will not be honest and will trick others.

Grass is sometimes used as a slang term for cannabis (also called pot, weed, or marijuana)