What term is used for a flat, level surface extending into space?

The term "plane" is used to describe a flat, level surface that extends infinitely in space in all directions. In geometry, a plane can be thought of as a two-dimensional surface without any thickness, and it is typically defined by three non-collinear points or by a line and a point not on that line. This concept is fundamental in various fields, including mathematics, physics, and engineering, as it provides a basis for understanding geometric properties and relationships.

The other terms do not convey the same meaning. An axis generally refers to a fixed reference line for measurement in geometry or three-dimensional space. A section typically refers to a specific part of something that has been divided or sliced, often used in the context of anatomy or geology. Level may describe the position of being even or flat, but it does not imply the infinite extent characteristic of a plane. Therefore, "plane" accurately encapsulates the concept of a flat surface in a geometric and spatial context.