Source control file created when an InDesign (.INDD) file is opened; allows the file to be "checked out" and prevents the InDesign document from being edited by more than one person at a time.

InDesign lock files typically use the following filename convention: "~[INDD filename]~[random string].idlk." They are saved in the same folder as the InDesign files they represent. Leftover IDLK files can be deleted after the InDesign application has been quit.