TDL is an extension given to files that are used by various applications, most often as a data source. Technically, TDL is a plain text file that can be opened in any editor. The structure of the TDL file is similar to the CSV format, with the difference that the file uses a tab character as a field (column) separator.

The most common use of TDL files is to import their data into spreadsheets. They can also be used as a data exchange format. The TDL extension can be used interchangeably with the TSV extension.