A format appearing in an input or output (I/O) statement specifies
  the form of data being transferred and the data conversion
  (editing) required to achieve that form.  The format specified can
  be explicit or implicit.

  Explicit format is indicated in a format specification that appears
  in a FORMAT statement or a character expression (the expression
  must evaluate to a valid format specification).

  The format specification contains edit descriptors, which can be
  data edit descriptors, control edit descriptors, or string edit
  descriptors.

  Implicit format is determined by the processor and is specified
  using list-directed or namelist formatting.

  List-directed formatting is specified with an asterisk (*);
  namelist formatting is specified with a namelist group name.

  List-directed formatting can be specified for advancing, sequential
  files and internal files.  Namelist formatting can be specified
  only for advancing, sequential files.