That might have been how it started (https://www.ibm.com/ibm/history/ibm100/us/en/icons/reldb/ https://www.ibm.com/ibm/history/ibm100/us/en/icons/reldb/). But

That might have been how it started (https://www.ibm.com/ibm/history/ibm100/us/en/icons/reldb/ https://www.ibm.com/ibm/history/ibm100/us/en/icons/reldb/). But it's definitely not what it means for the great majority of contemporary contexts. Relations in modern RDBMS are usually aliases to foreign keys unless otherwise specified.