Primary timeline

Centering on what the Time Lords called the "primary timeline" (AUDIO: Reborn) alternate timelines could diverge, which if left unchecked, would end the real universe millions of years before it was meant to due to there being only a finite amount of matter and energy in the uni-verse. Such a "sub-universe", the Silurian Earth, was destroyed by the Seventh Doctor. (PROSE: Blood Heat) Owen Harper told Rhys Williams that the Cardiff Space-Time Rift connected to not only other planets, but "other timelines". (TV: Meat)

Similarly, the Eleventh Doctor referred to the "natural timeline", which he helped to restore after the New Dalek Paradigm used the Eye of Time to change history. (GAME: City of the Daleks)