Open Peer Review on Qeios ## Polyhedron National Cancer Institute ## Source National Cancer Institute. Polyhedron. NCI Thesaurus. Code C73493. A polyhedron is a three-dimensional solid figure with flat polygonal faces, straight edges, and sharp corners or vertices. It is bounded by plane polygons or faces. Examples of polyhedrons include cubes, pyramids, and other geometric shapes with multiple faces. The term "polyhedron" comes from the Greek words "poly" meaning "many" and "hedron" meaning "face," reflecting the fact that it has multiple faces. Polyhedrons can be classified into different types, such as regular and irregular, convex and concave. A regular polyhedron is one where all faces are the same regular polygon and all edges are equal in length. Convex polyhedrons are those where all interior angles are less than 180 degrees, and any line segment between two points on the surface lies entirely within the polyhedron. In contrast, concave polyhedrons have at least one interior angle greater than 180 degrees. The study of polyhedrons is a fundamental part of geometry and has applications in various fields, including mathematics, engineering, and computer graphics.Open Peer Review on Qeios ## Polyhedron National Cancer Institute ## Source National Cancer Institute. Polyhedron. NCI Thesaurus. Code C73493. A polyhedron is a three-dimensional solid figure with flat polygonal faces, straight edges, and sharp corners or vertices. It is bounded by plane polygons or faces. Examples of polyhedrons include cubes, pyramids, and other geometric shapes with multiple faces. The term "polyhedron" comes from the Greek words "poly" meaning "many" and "hedron" meaning "face," reflecting the fact that it has multiple faces. Polyhedrons can be classified into different types, such as regular and irregular, convex and concave. A regular polyhedron is one where all faces are the same regular polygon and all edges are equal in length. Convex polyhedrons are those where all interior angles are less than 180 degrees, and any line segment between two points on the surface lies entirely within the polyhedron. In contrast, concave polyhedrons have at least one interior angle greater than 180 degrees. The study of polyhedrons is a fundamental part of geometry and has applications in various fields, including mathematics, engineering, and computer graphics.