A business rule is a rule that constrains some aspect of the business process.
According to the white paper by the Business Rules Group, a business rule falls in this category:
The most basic element of a business rule is the language used to express it. The very definition of a term is itself a business rule that describes how people think and talk about things. Thus, defining a term is establishing a category of business rule. Terms have traditionally been documented in a Glossary or as entities
E.g. a customer can place one or many order is a business rule. Facts can be documented as natural language sentences or as relationships, cardinality, attributes
Every enterprise constrains behaviour in some way, and this is closely related to constraints on what data may or may not be updated. To prevent a record from being made is, in many cases, to prevent an action from taking place.
The business rules can be completely represented in a logical data model
A business rule is known:
Example of a business rule for an application that will register submitted papers: