In databases, what is a one$-$to$-$one relationship?

A relationship in which a record in Table A can have multiple matching records in Table B$,$ but a record in Table B has only one matching record in Table A

A relationship in which no common field exists

A relationship in which each record in Table A can have only one matching record in Table B$,$ and vice versa

A relationship in which one record in Table A can relate to many matching records in Table B$,$ and vice versa