You start a command like OPEN or SAVEAS, and instead of a pop-up to select file location and name, you get prompted at the command line to manually enter the information.
FILEDIA variable is turned off: at the command line, type it and when ask, type 1 (one) to turn it on. This variable is designed to suppress display of file navigation dialog boxes if set to 0 (zero).
It affects many other commands, including BMPOUT, CUILOAD, CUIUNLOAD, IMPORT, JPGOUT, NEW, OPEN, PNGOUT, PUBLISH, RECOVER, RECOVERALL, SAVEAS, SCRIPT, TIFOUT, VSLIDE, WBLOCK and XREF among others.
A similar variable, CMDDIA, used to affect more commands in older LT versions, but in many of the latest versions only affect QLEADER;s in-place text editor.