In
planar geometry, an
angle is the figure formed by two
rays, called the
sides of the angle, sharing a common endpoint, called the
vertex of the angle. Angles formed by two rays lie in a plane, but this plane does not have to be a
Euclidean plane. Angles are also formed by the intersection of two planes in
Euclidean and other spaces. These are called
dihedral angles. Angles formed by the intersection of two curves in a plane are defined as the angle determined by the tangent rays at the point of intersection. Similar statements hold in space, for example, the
spherical angle formed by two
great circles on a
sphere is the dihedral angle between the planes determined by the great circles.