Geometry is a branch of mathematics that deals with the study of shapes, sizes, angles, and properties of objects in space. It is concerned with the measurement and properties of lines, angles, surfaces, and solids. Geometry is used in a wide variety of fields, including physics, engineering, architecture, and computer science, to solve problems related to spatial relationships and geometric forms. Some key topics in geometry include Euclidean geometry, non-Euclidean geometry, trigonometry, and topology.