A flat was a form of housing on Earth.
Jackie Tyler owned a flat on the Powell Estate in which she lived with her daughter Rose. (TV: Rose) They lived in number 48 of Bucknall House. (TV: Love & Monsters)
Martha Jones owned a flat during her residency at Royal Hope Hospital. (TV: The Lazarus Experiment) The Master had a bomb planted in her flat. (TV: The Sound of Drums)
Gwen Cooper and Rhys Williams lived in a flat together. (TV: Everything Changes)
Craig Owens had a flat on Aickman Road. He briefly shared the flat with the Eleventh Doctor. (TV: The Lodger)