Encounter "(+)" in the SQL statement in Oracle )"

I have never seen such writing before, such

Select * from t_spolicy d, V_POLICYEMPLOYEE g where d. policyno = g. policyno (+)

Only by checking relevant information can we find that this method is another form of external connection, which is equivalent

Select * from t_spolicy d left join V_POLICYEMPLOYEE g on d. policyno = g. policyno,

Similarly, select * from t_spolicy d, V_POLICYEMPLOYEE g where d. policyno (+) = g. policyno,

It is equivalent to select * from t_spolicy d right join V_POLICYEMPLOYEE g on d. policyno = g. policyno