Difference between foreign key and reference key

What is the difference between foreign key and reference key ?

Foreign key is the key i.e. attribute which refers to another table primary key. Reference key is the primary key of table referred by another table.

Can dual table be deleted, dropped or altered or updated or inserted ?

Yes

If content of dual is updated to some value computation takes place or not ?

Yes

If any other table same as dual is created would it act similar to dual?

Yes

For which relational operators in where clause, index is not used ?

<> , like '% ...' is NOT functions, field +constant, field || ''

Assume that there are multiple databases running on one machine. How can you switch from one to another ?

Changing the ORACLE_SID