A constant is a data item with a fixed value that cannot be changed during program execution. The value of a constant can be a numeric value, a logical value, or a character string. A constant can be any of the following types:
The term scalar reference is applied to all references that resolve into a single data item having a data type. References to any of the preceding types of constants are scalar references.
For details on scalar references, see Section 2.2.6.