From Oracle FAQ
A constant as the name implies is a value that is not variable. It cannot be changed after it has been assigned to. By virtue of the fact that it cannot be modified a constant cannot be declared without also being initialised.
 PL/SQL Example
DECLARE -- c_someConstant CONSTANT NUMBER; -- ILLEGAL since no initial value has been supplied. c_report_lines CONSTANT NUMBER := 80; -- Define a numeric constant BEGIN dbms_output.put_line('Report has '||c_report_lines||' lines'); END; /
 Also see
|Glossary of Terms|