The document discusses the relational model of data, which is based on relations. A relation is a mathematical concept like a table with rows and columns. Each column has an attribute name and each row contains a tuple of values. The key uniquely identifies each tuple. An example relation shown is the STUDENT table with attributes like SSN. A relation's schema defines its name and attributes. Tuples contain ordered values from the appropriate domains. The relation state is a subset of the Cartesian product of the domains.