Bamboos are a diverse group of mostly evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family, in the case of Dendrocalamus sinicus individual culms reaching a length of 151 feet (46 meters), up to fourteen inches (36 centimeters) in thickness and a weight of up to 990 pounds (450 kilograms). The internodes of bamboos can also be of great length. Kinabaluchloa wrayi has internodes up to 8.2 feet (2.5 meters) in length. and Arthrostylidium schombergkii with lower internodes up to 16 feet ( five meters) in length, exceeded in length only by Papyrus. By contrast, the culms of the tiny bamboo Raddiella vanessiae of the Kaieteur Plateau in French Guiana are only 0.4–0.8 inches (10–20 millimeters) in length by about one-twelfth inch (two millimeters) in width. The origin of the word "bamboo" is uncertain, but it probably comes from the Dutch or Portuguese language, which originally borrowed it from Malay or Kannada.

In bamboo, as in other grasses, the internodal regions of the stem are usually hollow and the vascular bundles in the cross-section are scattered throughout the walls of the culm instead of in a cylindrical cambium layer between the bark (phloem) and the wood (xylem) as in Dicots and Conifers. The dicotyledonous woody xylem is also absent. The absence of secondary growth wood causes the stems of monocots, including the palms and large bamboos, to be columnar rather than tapering.

Bamboos include some of the fastest-growing plants in the world, due to a unique rhizome-dependent system. Certain species of bamboo can grow 91 centimetres (36 inches) within a 24-hour period, at a rate of almost 40 millimeters (1+1⁄2 in) an hour (equivalent to 1 mm every 90 seconds). Growth up to 47.6 inches (156 centimeters) in 24 hours has been observed in the instance of Japanese giant timber bamboo (Phyllostachys bambusoides). This rapid growth and tolerance for marginal land, make bamboo a good candidate for afforestation, carbon sequestration and climate change mitigation.

Bamboo is versatile and has notable economic and cultural significance in South Asia, Southeast Asia, and East Asia, being used for building materials, as a food source, and as a raw product, and depicted often in arts, such as in bamboo paintings and bambooworking. Bamboo, like wood, is a natural composite material with a high strength-to-weight ratio useful for structures. Bamboo's strength-to-weight ratio is similar to timber, and its strength is generally similar to a strong softwood or hardwood timber. Some bamboos have displayed remarkable strength under test conditions. Bambusa tulda of Bangladesh and adjoining India has tested as high as 60,000 pounds (27,000 Kg or 27 tonnes) per square inch in tensile strength. Other bamboos have extraordinailly hard wood. Bambusa tabacaria of China contains so much silica that it will make sparks when struck by an axe.