Cardinality is defined as follows in my school text Database Systems:
A relation's cardinality is the number of tuples it contains. The cardinality of the relation, on the other hand, refers to the number of tuples in the relation, which changes when tuples are added or removed. Many tuples in high-cardinality, few tuples in low-cardinality.
Cardinality (SQL statements) is defined as follows in the Wikipedia article:
The uniqueness of data values included in a single column (attribute) of a database table is referred to as cardinality. In a column, the smaller the cardinality, the more duplicated components there are. Cardinality is divided into three categories: high cardinality, normal cardinality, and low cardinality.
They might both be correct, but I can't see how the two definitions are linked. A response would be much appreciated!