An office was a room, typically used for business work.
The Doctor had several offices throughout their lives. The Sixth Doctor had an office at Bletchley Park. Constance Clarke asked why he kept his TARDIS in his office when he could keep his office in his TARDIS. (AUDIO: Criss-Cross) The Eighth Doctor had an office during his time as the owner of St Louis Bar and Restaurant. (PROSE: Escape Velocity) They had previously wanted an office whilst working with UNIT in their eleventh incarnation. (TV: The Day of the Doctor) In their twelfth incarnation, while lecturing at St Luke's University, the Doctor had an office on the campus. (TV: The Pilot, et al.) The Thirteenth Doctor had an office whilst she worked as a museum curator in Venice. (PROSE: The Liar, the Glitch and the War Zone)
By 1994, the underfunded and understaffed P.R.O.B.E. was based in a single office at Ashley House that Dr Liz Shaw described as being cramped. She had a blackboard in there and had newspaper articles relating to UNIT and its exploits during and before her career there on the wall, as well as a photograph of Alistair Gordon Lethbridge-Stewart. (HOMEVID: The Zero Imperative)