(physics) the rule which states that the number of degrees of freedom in a system at equilibrium equals the number of components minus the number of phases plus 2

(law) The rule stating that an unborn child, if subsequently born alive, is considered as already in existence whenever it is to its own advantage.

(computing, of a computing language, or expert system) based on a series of simple "if then" rules

(sports) A rule that ends a one-sided contest prior to its natural conclusion.

(physics) Any of several general rules concerning the transitions between the states of a quantum mechanical system; they derive from the symmetry properties of the states and of their interactions

Alternative form of McNaughton rules

A general guideline, rather than a strict rule; an approximate measure or means of reckoning based on experience or common knowledge. / (attributive, usually hyphenated) Approximated, guesstimated.

Rule of a group of people by their own leaders as opposed to rule imposed by a foreign government or people.

(idiomatic) To work slowly by strictly following all work rules, usually in a work-to-rule job action, as part of unionized labor protest.

Alternative spelling of work-to-rule