Litter consists of waste products that have been disposed improperly, without consent, at an inappropriate location. Litter can also be used as a verb. To litter means to drop and leave objects, often man-made, such as aluminum cans, cardboard boxes or plastic bottles on the ground and leave them there indefinitely or for others to dispose of as opposed to disposing of them properly.

Large and hazardous items of rubbish such as tires, electrical appliances, electronics, batteries and large industrial containers are sometimes dumped in isolated locations, such as national forests and other public land.

It is a human impact on the environment and is a serious environmental issue in many countries. Litter can exist in the environment for long periods of time before degrading and be transported large distances into the world's oceans. Litter can affect quality of life.

Cigarette butts are the most littered item in the world, with 4.5 trillion discarded annually. Estimates on the required time for cigarette butts to break down vary. They range from five years to 400 years for complete degradation.

A birth colony is the offspring at one birth of animals from the same mother and usually from one set of parents. The word is most often used for the offspring of mammals, but can be used for any mammal that gives birth to multiple young. Biology In comparison, a group of eggs and the offspring that hatch from them are frequently called a clutch, while young birds are often called a brood. A litter is defined as anywhere between three and eight offspring.

Animals from the same litter are referred to as litter-mates.

Animals frequently display grouping behavior in herds, swarms, flocks, or colonies, and these multiple births derive similar advantages. A litter offers some protection from predation, not particularly to the individual young but to the parents' investment in breeding. With multiple young, predators could eat several and others could still survive to reach maturity, but with only one offspring, its loss could mean a wasted breeding season. The other significant advantage is the chance for the healthiest young animals to be favored from a group. Rather than it being a conscious decision on the part of the parents, the fittest and strongest baby competes most successfully for food and space, leaving the weakest young, or runts, to die through lack of care.

A litter is a stretcher or basket designed to be used where there are obstacles to movement or other hazards: for example, in confined spaces, on slopes, in wooded terrain. Typically it is shaped to accommodate an adult in a face up position and it is used in search and rescue operations. The person is strapped into the basket, making safe evacuation possible. The person generally is further protected by a long spine board and a cervical collar, so as to immobilize the person and prevent further injury.

A litter essentially is a stretcher with sides (or just a raised edge) and a removable head/torso cover. They are most notably remembered from Korea and Vietnam images of United States Air Force Pararescue airmen or more recent Coast Guard video clips of helicopters rescuing injured people from isolated areas. Some will also recall the images from the TV shows Emergency! & M*A*S*H of fixed stretchers on either side of medical evacuation helicopters.

One widely used style of litter is the Stokes basket.