Online mode is normal mode used when user is programming less number of chips (preferred for development purpose). All the functions such as buffer edit are enabled in online mode.
Terminal mode is a special mode designed for factory volume production which is used rarely. This mode only allows a few functions (such as Auto) to prevent operation errors from destroying the chips or to prevent wrong data from being written to the chip. The project file should be loaded into SD card, and the programmer is controlled using software commands (and not using keypad on the Superpro 7500 programmer)