Which term is used to describe a two-dimensional figure that extends infinitely?

The term that describes a two-dimensional figure that extends infinitely is a plane. In geometry, a plane is defined as a flat surface that has no thickness and extends forever in all directions. It can be visualized as a sheet of paper that continues indefinitely beyond its edges. This is a fundamental concept in geometry, as planes are used to define various shapes and forms, serving as the foundational backdrop for geometric figures.

Other options present different concepts: a surface generally refers to the outer layer or boundary of an object and can exist in three dimensions, volume measures the amount of space inside a three-dimensional object, and a line is a one-dimensional figure that extends infinitely in two directions but does not have thickness or breadth. Thus, none of these alternatives accurately captures the characteristics of a two-dimensional figure that extends infinitely.