Old Time

The Old Time refers to the time on Gallifrey before Rassilon had created the Time Lord civilisation. In this time, Rassilon fought the vampires throughout the Universe (TV: State of Decay) and with Omega created the Eye of Harmony (TV: The Three Doctors), validium (TV: Silver Nemesis), and the Hand of Omega. (TV: Remembrance of the Daleks)

Gallifreyans had the ability to reproduce during the Old Time. When the Pythia cursed them with infertillity, they created Looms. (PROSE: Lungbarrow)

Lady Peinforte threatened to reveal the Doctor's secret "from the Old Time". (TV: Silver Nemesis)

The Doctor told the Mi'en Kalarash the he was afraid of the old time, that he remembered it and feared it's return. (AUDIO: House of Blue Fire (audio story))

There is speculation about if this secret may be the nature of the Doctor's birth, as revealed in TV: Doctor Who by the Doctor. Russell T Davies, in an earlier script for TV: The End of Time, would have discounted this idea by having the Doctor say it was a "48-hour bug." (Doctor Who Confidential)