A bust was a sculpture of a person's head.
Morbius once had a clay bust of himself, representing a head that he once had. (TV: The Brain of Morbius)
The Doctor kept a bust of Napoléon Bonaparte in the TARDIS console room. (PROSE: Doctor Who in an Exciting Adventure with the Daleks, Doctor Who and the Crusaders, State of Change, Shadowmind)
The Twelfth Doctor kept a bust of Beethoven aboard his TARDIS. (TV: Before the Flood) During his time as lecturer at St Luke's University in Bristol, he moved the bust into his office, alongside his bust of William Shakespeare. (TV: The Pilot)
Whilst visiting one of the first human colonies, Bill Potts found a bust of Queen Nefertiti amongst the crew's possessions. (TV: Smile)