(algebra) An integral domain which has a subset whose elements are said to be "positive", such that this subset is closed under addition, closed under multiplication, and all elements of the integral domain satisfy a law of trichotomy; namely, that either that element is in the said subset, or it is the zero (additive identity), or its product with −1 (the additive inverse of the multiplicative identity) belongs to the said subset.

(mathematics) An ordered field which satisfies the axiom of Archimedes.

(astronomy) The sidereal year of a planet. (I.e., in the definition for "sidereal year", replace "Earth" by the given planet.)

The orbit of an object around the moon.

(chemistry, physics) A molecular orbital, responsible for a covalent bond between two atoms, formed by overlap of their corresponding atomic orbitals

(chemistry) The number of bonds between a pair of atoms in a molecule

(physics, chemistry) A method of determining the structure of a molecule by assuming that electrons are not fixed to bonds between individual atoms

An order that cannot be currently filled or shipped, but is requested nonetheless for when the item becomes available again.

To treat as a back order.

(inorganic chemistry) A complex, typically of a transition element, in which the hybridization of the central metal atom utilizes d orbitals from the shell inside that of the outermost occupied shell