An ancestor was any lifeform from whom another was descendant. (TV: The Daleks, The Web Planet et al.) As such, ancestors were parents, followed by grandparents.
Nyssa of Traken asked Tegan Jovanka, a human, if dinosaurs were her ancestors, to which she replied that she hoped not. The Fifth Doctor, however, told Tegan that she should have been proud if they were. He later informed her that the evolutionary stage of her ancestors circa 65,000,000 BC was "very primitive". (TV: Earthshock)
Trojan King Priam recalled that his ancestors came from central Asia. (TV: The Myth Makers)
The bat-shaped Krillitane inherited their wings from their ancestors who invaded Bessan. (TV: School Reunion)
Traveling back to Earth in the year 2008, the Toclafane slaughtered their human ancestors. However, they were protected by the temporal reprecussions of this act by the Paradox machine created by the Master, beginning the Year That Never Was. (TV: The Sound of Drums/Last of the Time Lords)
The Fourth Doctor noted that 5000 AD, the year of humanity's Great Breakout, was still in the time of Leela's ancestors. (TV: The Invisible Enemy)
Jabe of the Forest of Cheem recalled that her ancestors were transplanted from Earth prior to Earth Death. (TV: The End of the World)