An office was a room, typically used for business work.
The Doctor had several offices throughout their lives. 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)