1. A direction perpendicular to one of the faces of a crystal.

2. One of the points at which normals to crystal faces or planes intersect a reference sphere at whose center the crystal is located.

1. One of the electrodes in an electric cell.

2. An output terminal on a switch; a double-pole switch has two output terminals.

1. An isolated singular point z₀ of a complex function whose Laurent series expansion about z₀ will include finitely many terms of form a_n(z-z₀)^-n.

2. For a great circle on a sphere, the pole of the circle is a point of intersection of the sphere and a line that passes through the center of the sphere and is perpendicular to the plane of the circle.

3. For a conic section, the pole of a line is the intersection of the tangents to the conic at the points of intersection of the conic with the line.

4. For a quadric surface, the pole of a plane is the vertex of the cone which is tangent to the surface along the curve where the plane intersects the surface.

5. The origin of a system of polar coordinates on a plane.

6. The origin of a system of geodesic polar coordinates on a surface.

1. A point at which an axis of rotation or of symmetry passes through the surface of a body.

2. See <<perch>>

1. The geometric center of a convex or concave mirror.

2. See <<optical center>>