Riemannian geometry is a branch of differential geometry that studies smooth manifolds equipped with a Riemannian metric, which allows for the measurement of distances and angles within the manifold. It is named after the German mathematician Bernhard Riemann, who laid the foundations for this field in the 19th century. Riemannian geometry has applications in various areas of mathematics and physics, including general relativity, differential topology, and geometric analysis. It plays a crucial role in understanding the geometry of curved spaces and is essential for describing the curvature of surfaces and higher-dimensional manifolds. Key concepts in Riemannian geometry include geodesics (the analogs of straight lines in curved spaces), curvature tensors, and the Riemann curvature tensor, which captures the intrinsic geometry of a Riemannian manifold. The study of Riemannian geometry also involves investigating properties such as volume, area, and shape of geometric objects in a curved space. Overall, Riemannian geometry provides a powerful framework for studying the geometry of spaces with variable curvature, and it has far-reaching implications in diverse fields of mathematics and physics.