What do we call the number of square units inside a 2-dimensional figure?

The number of square units inside a two-dimensional figure is referred to as the area. Area measures the extent of a surface and quantifies how much space is contained within the boundaries of a shape, such as rectangles, triangles, circles, and other polygons. It is typically calculated using specific mathematical formulas depending on the figure type, for example, length times width for rectangles or π times radius squared for circles.

Perimeter, on the other hand, refers to the total distance around the outside of a figure, which is not what is being asked in this question. Circumference is specifically the term used for measuring the distance around a circular shape. Volume pertains to three-dimensional figures and measures the amount of space they occupy, which is also not relevant to the context of a two-dimensional figure. Therefore, the correct term for what is being described in the question is indeed area.