What concept describes how instances of one entity relate to instances of another entity?

The concept that describes how instances of one entity relate to instances of another entity is cardinality. In the context of database design and systems analysis, cardinality refers to the number of instances of one entity that can or must be associated with instances of another entity. For example, in a relationship between a "Customer" entity and an "Order" entity, cardinality can specify that one customer can have many orders, but each order can be associated with only one customer. This understanding is crucial for designing databases that accurately reflect the real-world relationships between different entities.

While dependency, association, and multiplicity also deal with relationships between entities, they do not precisely capture the essence of how many instances of one entity correspond to another. Dependency typically refers to relationships where one entity relies on another, association indicates a general relationship between entities without specifying the number of instances, and multiplicity, while related, is often used in the context of UML diagrams to describe the numeric aspect within an association. Thus, cardinality is the most accurate term for describing the specific quantitative relationship between different entities in a system.