%TYPE:
This attribute gives the datatype of a formerly declared collection, cursor variable, object, field, record, database column, or variable.
Datatype:
This is simply a type specifier.
Expression:
This is a randomly complex combination of the constants, variables, literals, function calls, and operators. The simplest expression consists of the single variable. If the declaration is explained, the value of the expression is assigned to the parameter. The value and the parameter should have compatible datatypes.