Final answer:
The proportion, by mass, of pre-consumer or postconsumer recycled material in a product is defined by the ISO 14021 standard. It is used to measure the percentage of recycled material used and is commonly used for environmental labeling.
Step-by-step explanation:
The proportion, by mass, of pre-consumer or postconsumer recycled material in a product is defined by the ISO 14021 standard. This standard is used to measure the percentage of recycled material used in a product and is commonly used for environmental labeling. For example, a product labeled with ISO 14021 may indicate that it contains 50% postconsumer recycled material, meaning that 50% of the material used in the product was recycled from consumer waste.