Geometry is a branch of mathematics that focuses on the study of points, lines, angles, surfaces, and solids.
In high school, students will mostly study Euclidean geometry.
Euclidean geometry is the geometry of flat planes, straight lines, and points.
Beyond high school, students may study spherical geometry.
In spherical geometry, a plane is no longer flat but it is the curved surface of a sphere and a line is now a great circle on the sphere.