A law, which may informally be called a "rule"

Moral summary and related information.

Norm (sociology), an informal but widely accepted rule, concept, truth, definition, or qualification (social norms, legal norms, coding norms)

Ja Rule, a hip hop artist

In ethics, the Golden Rule is a principle of reciprocity common throughout all or most religious or otherwise cultural systems: see ethic of reciprocity

Standardization, a formal and widely-accepted statement, fact, definition, or qualification

Rules of Acquisition, a set of guidelines intended to ensure the profitability of businesses owned by the ultra-capitalist Ferengi in the fictional Star Trek universe

"Rulership" is the concept of governance by a government:

Rule, a component of an astrolabe, circumferator or similar instrument.

Heuristic, a quantized "rule" which shows a tendency or probability for successful function

Operation, a determinate rule (method) for performing a mathematical operation and obtaining a certain result (Mathematics, Logic)

Norm (philosophy), a kind of sentence or a reason to act, feel or believe.

Rule of inference, a function from sets of formulae to formulae (Mathematics, Logic)

Rule of thumb, an idiom for an estimation procedure

Rule engine, a software system that helps managing business rules

Procedural law, a ruleset governing the application of laws to cases

Binary operation

The Rules, a bestselling self-help book

Golden rule (law), a rule for the construction of statutes in British law

Rule, an instrument for measuring lengths

R.U.L.E., a 2005 greatest hits album by rapper Ja Rule

Moral, an atomic element of a moral code for guiding choices in human behavior

A regulation, as in sports

A court ruling, a decision by a court

Rule, in Graphic Arts, a horizontal line across a page.

Unary operation

RULE Project (Run Up-to-date Linux Everywhere) is a project that aims to use up-to-date Linux software on old PCs

Military rule, governance by a military body

In generative grammar and computer science, a rewrite rule.

Monastic rule, a collection of precepts that guides the life of monks or nuns in a religious order where the superior holds the place of Christ

Rule (song), a song by rapper Nas

The Rule, an American, pop/R&B band.