A Fixed Width File is set of records where the columns are defined with a specific number of characters. There are no special character that separates the columns.
The Fixed Width File sample shown below is similar data as the delimited file, however, the columns starts and ends at a specific point.
In some cases your client might provide you with more detailed information. This can be used while mapping your data for your Import Mapping Definition (IMD) or Temporary Mapping Definition (TMD).