The term "waste stream" refers to all the materials that are discarded or considered unwanted. This includes solid waste, such as garbage and trash, as well as liquid waste, like sewage and industrial effluent. The waste stream also encompasses gaseous emissions from various sources, including factories, vehicles, and power plants. In essence, the waste stream is a collection of all materials that are no longer useful or needed by society, and it presents significant environmental challenges due to its impact on air, water, and land resources.