What does cardinality specify in an entity-relationship diagram (ERD)?

Cardinality in an entity-relationship diagram (ERD) specifies the number of instances in relationships between entities. It defines how many instances of one entity can or must be associated with each instance of another entity. For example, in the relationship between a customer and their orders, cardinality can indicate whether a customer can have one or many orders and whether each order is associated with just one customer or can be linked to multiple customers in specific contexts.

Understanding cardinality is crucial for database design as it helps establish the rules for how entities are related, which in turn affects how data is organized and the integrity of relationships within the database. This ensures that data is accurately represented and efficiently queried, avoiding potential anomalies in data management. Thus, option C accurately reflects the role of cardinality in ERDs.