You base a declaration on a table column without having to know definitively what that column's datatype is.
Your variables will automatically be changed as the table column.
You use the %type attribute in variable declarations to define variable based on table column.
avg_rate employee.pay_rate%type
dept_id INTEGER;
sub_dept_id dept_id%type; -- datatype based on a variable
area_id dept_id%type := 9141; -- used with an initialization clause