(crystallography) A plane of molecular weakness that allows movement without fracture.

A general-purpose bench plane, used for general sizing of wood and for smoothing or straightening edges.

(engineering) A plane which serves as a reference or base for the measurement of other quantities.

(nautical) A technique for navigation using planar geometry. / (nautical, proscribed) A technique for navigation using the assumption the Earth is flat.

(geology) The planar surface between adjacent strata

(anatomy) Any vertical plane that divides the body into anterior and posterior (belly and back) sections.

(anatomy) Any plane that divides the body into superior and inferior parts, roughly perpendicular to spine.

(anatomy) Any plane that divides the body into superior and inferior parts, roughly perpendicular to spine.

(set theory) The Cartesian product of two real lines.

(mathematics) Either half of an infinite plane (divided by a straight line)