Any of a system of coordinates by which a point is located in space by its distance from a pole, the angle between the polar axis and its radius vector, and its longitude

(obsolete) The volume of the conducting airways of the lung. This definition became inadequate once the alveolar dead space was described.

(anatomy) That volume of conducting airways of the lung, as measured by a cast of the airways.

(physiology) The volume of air in the alveoli of the lung which does not partake in the exchange of gas.

The dark space in a glow discharge between the cathode glow and the negative glow.

(mathematics) A vector space which is additionally equipped with a norm.

(mathematics) A vector space which is additionally equipped with an inner product.

The quotient of a Hilbert space by an equivalence relation which considers a pair of vectors equivalent iff they differ only by a factor which is a complex number.

The dark space in a glow discharge that is between the negative glow and the positive column.

The dark space in a glow discharge that is adjacent to the cathode.