Español: Razón / Português: Razão / Italiano: Rapporto
A Ratio is the relationship in quantity, amount, or size between two or more things.

In the environment context, a "ratio" refers to the relationship or proportion between two or more quantities. Ratios are commonly used to compare and evaluate various environmental indicators such as pollution, resource use, and biodiversity.

For example, a common ratio in the environmental context is the ecological footprint, which is a measure of the impact of human activities on the earth's resources. It is calculated as the ratio of the area of land and water required to produce the resources consumed by a population, to the area of land and water available within a region.

Another example is the carbon footprint, which measures the amount of greenhouse gases emitted by an individual, organization, or product, typically measured in units of carbon dioxide equivalents (CO₂). It’s a ratio of the total amount of carbon dioxide and other greenhouse gases emitted, to a unit of measurement (e.g. per person per year).

Additionally, another ratio that could be used in the environment context is resource use efficiency ratio, this ratio compares the inputs of resources such as energy, water, and materials, to the outputs of goods and services in a production process. It's used to evaluate the level of waste and resource efficiency in an organization.

In mathematics, a ratio is a relationship between two numbers of the same kind (e.g., objects, persons, students, spoonfuls, units of whatever identical dimension), usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two that explicitly indicates how many times the first number contains the second (not necessarily an integer).