I believe the answer to this is "area." It is fairly vague and I would need the context of the question to be sure.
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The measure of a plane region is usually expressed in square units, such as square meters or square feet. This unit indicates the area covered by the region on a flat surface.
The intensity of a wave is usually measured as the power transmitted through a unit area perpendicular to the direction of wave propagation. It is usually expressed in watts per square meter (W/m^2) and is proportional to the square of the amplitude of the wave. Stronger waves have higher intensity levels.
Area is the measure of the two-dimensional space enclosed by a shape or object. It is usually expressed in square units, such as square meters (m²) or square feet (ft²). Area is calculated by multiplying the length of a shape by its width.
Square meters is a measure of area and must be expressed in square feet, not simply feet. Six square meters is 64.6 square feet
Area units measure the amount of space that a two-dimensional shape covers. It is typically expressed in square units, such as square meters, square feet, or square centimeters. The larger the value of the area unit, the greater the space occupied by the shape.
The measure of the number of people or other life forms in a specific area is called population density. It is usually expressed as the number of individuals per unit area, such as per square kilometer or square mile. Population density helps geographers understand how crowded or sparse an area is in terms of human or animal inhabitants.