Kellogg's terminal password

 is a holodisc that can be discovered and obtained within the Commonwealth in Fallout 4. It can be found Fort Hagen, and must be looted off of the corpse of Kellogg. This holotape is necessary to progress the main story, as this password is needed in order to access Kellogg's nearby terminal, which can be used to unlock the mag-locked doors leading back outside.