The epipole is the image in one camera of the optical centre of the other camera. Or, equivalently, by an image point and the optical centres. It is the image in one camera of a ray through the optical centre and image point in the other camera. All epipolar lines intersect at the epipole. This family of planes is known as an epipolar pencil.
All epipolar lines intersect at the epipole.
A point in one image generates a line in the other on which its corresponding point must lie. The search for correspondences is thus reduced from a region to a line. This epipolar constraint arises because, for image points corresponding to the same 3D point, the image points, 3D point and optical centres are coplanar.