A fake was an object that was not genuine.
History
In an interview hosted by Mickey for his website in early 2006, Henry Van Statten stated that the Gray Market was "easy pickings for fakes and loons", but he learnt to recognise the real alien artefacts. (PROSE: Henry Van Statten [+]BBC webteam, Who is Doctor Who? (BBC, 2005).)
The Fourteenth Doctor identified the not-thing which imitated his form as a "fake". (TV: Wild Blue Yonder [+]Russell T Davies, Doctor Who 60th Anniversary Specials (BBC One and Disney+, 2023).)