What type of waste does the term 'Wastewater' refer to?

The term 'Wastewater' specifically refers to water that has been used and contaminated, typically through various processes, including domestic, agricultural, or industrial activities. In the context of the given options, this refers predominantly to sewage, which is composed of water mixed with animal or vegetable matter that arises from household or commercial use.

This definition is important because wastewater treatment focuses on removing contaminants from sewage to prevent pollution and protect water resources. It incorporates various organic and inorganic materials, leading to the classification of wastewater. Other types of waste mentioned, such as solid waste from landfills, industrial effluent, and plastic waste, do not capture the specific characteristics of wastewater, which are primarily related to water that has been used and contains organic matter.