A constant is a fixed value.  The value of a constant can be a
  numeric value, a logical value, or a character string.

  A constant that has a name is a named constant.  A named constant
  can be of any type, including derived type, and it can be
  array-valued.  A named constant has the PARAMETER attribute and is
  specified in a type declaration statement or PARAMETER statement.

  A constant that does not have a name is a literal constant.  A
  literal constant must be of intrinsic type and it cannot be
  array-valued.

  There are nine types of literal constants:  integer, real, complex,
  binary, octal, hexadecimal, logical, character, and Hollerith.
  Binary, octal, hexadecimal, and Hollerith constants have no data
  type; they assume a data type that conforms to the context in which
  they are used.