In MFA, the term "materials" is often used in a broad sense, so as to encompass all material-related flows arising at all stages of the material cycle. It refers to both materials and products derived from natural resources that are used as inputs into human activities, as well as residuals (such as waste or pollutant emissions) arising from their extraction and use, and ecosystem inputs (such as nutrients, carbon dioxide, and oxygen) required for their extraction and use. Here the focus is on “material resources” that designate the usable materials or substances (raw materials, energy) produced from natural resources.