How is the number of rows in a relation referred to?

The number of rows in a relation is referred to as "cardinality." In the context of database design, cardinality specifically describes the count of tuples (or records) in a relation (or table). Each tuple represents a unique data row, and cardinality is an essential concept that helps in understanding the size and scalability of a database.

This term is crucial when considering database normalization and the design of data structures, as it influences how data is organized, indexed, and queried. Proper management of cardinality can help optimize performance and ensure that a database operates efficiently, especially as it scales. The other terms in the choices refer to different concepts; for instance, "degree" refers to the number of attributes (columns) in a relation, while "multiplicity" and "count" do not specifically relate to the definition of rows within the relational model.