|the study of the properties of and relationships between plane curves, figures, etc|
The mathematical study of geometric figures whose parts lie in the same plane, such as polygons, circles, and lines.
The study of two-dimensional figures (figures that are confined to a plane).
Note: Plane geometry is one of the oldest branches of mathematics.
Note: The Greek mathematician Euclid was the first to study plane geometry carefully. His book Elements was the standard plane geometry textbook for centuries.