The most commonly encountered timeline is known as the "canon" universe or "primary" universe. The history of this reality includes the known history of Earth, the Federation, with events known until around the Terran year 2379. While generally continuous in and of itself, there are numerous time-travel scenarios and other reality-distorting events that have created discontinuities that, in some respects, could be considered parallel universes or timelines.
This alternate reality diverged from the primary universe in early 2372 after Admiral James Leyton's coup on Earth was successful and triggered the start of a Federation Civil War. (Star Trek: Pendragon)
This alternate reality diverged from the primary universe at an unknown time before humanity's discovery of warp drive, yet the reality was similar to the prime universe in many ways. (Star Trek: Remington)