Alternate universe
Any one of many parallel timelines created by differing decisions made by presumably anyone in the Universe. Also known as a "Parallel Universe" or the known, separate "Mirror Universe," these are often self-contained, co-existing with, and not overlapping any others. Alternate universes, or "alternate reality" timelines can be accessed or created due to time travel, dimension-hopping, or through the powers of a Q being. The study of such realities or universes is also known as the "Multiverse Theory."
The Mirror Universe is one alternate timeline that runs parallel to our own, and though historical events are slightly or deeply altered, still manages to have roughly the same occupying population. Captain Kirk and Captain Sisko have both visited the same alternate universe, existing perhaps in a dimension directly next to our own. They were both made aware of their counterparts and those of others, and all decided to stay in their own universes / dimensions.
For example, in this playable Universe, your character may be a Starfleet Officer. In an alternate timeline or universe, your character could be dead, or a spy for the warring Pakled Empire.
