A filing cabinet was a type of furniture used to store paper documents.
While the Master was trying to use the Nurazh to take over the Earth, his TARDIS was disguised as a filing cabinet. (PROSE: The Touch of the Nurazh)
The Doctor's files concerning "Project: Twilight" were listed under "T" in the TARDIS' filing cabinet. (AUDIO: Project Destiny)
While Berenyi was arranging the assassination of John F. Kennedy, her TARDIS was disguised as a filing cabinet. (PROSE: Untitled)