Relational Model Definitions:
A relation is a table with columns and rows.
An attribute is a named column of a relation.
A tuple is a row of a relation.
A domain is a set of allowable values for one or more attributes.
The degree of a relation is the number of attributes it contains.
The cardinality of a relation is the number of tuples it contains.
A relational database is a collection of normalized relations with distinct relation names.
The intension of a relation is the structure of the relation including its domains.
The extension of a relation is the set of tuples currently in the relation.
https://cmps-people.ok.ubc.ca/rlawrenc/teaching/304/Notes/304_3_Relational_by6.pdf
https://dsf.berkeley.edu/jmh/cs186/f02/lecs/lec4_2up.pdf