Alternate Timeline

''"What if it were possible to shape and mold time as you would a ball of clay? What possibilities await? What new worlds could we create?" - ''Kairozdormu

An Alternate Timeline is an alternate realm similar to the existing and "original" timeline most of the known history takes place in. Alternate timelines typically diverge greatly in some aspect of history and its outcomes.

Alternate timelines mostly exist out of the simple calculations of what could happen differently in another existence, but sometimes alternate timelines are unnaturally made by Chronomancers. Chronomancers (with the term of Chronomancy referring to the magical manipulation of time) are sometimes capable of tearing open a rift between two timelines and are able to alter history from that point forward.

Examples of Alternate Timelines
Alternate Draenor - The world of Draenor altered by the changes instilled within the newly formed Orcish Horde by Garrosh Hellscream. The result was a Draenor untouched by demonic magic and ruled by the Iron Horde. The gap between Alternate Draenor and the "original timeline" was bridged during the Iron Horde invasion of Azeroth. Garrosh reached this timeline with the aid of Kairozdormu's Chronomancy.

Dalaranian Azeroth - Azeroth unaffected by the Undead Scourge and the Burning Legion after Margrave Haifrall prevented the coming of the Third War. This, along with Margrave's counsel, resulted in Azeroth being ruled by a single magical Empire of Dalaran known as the Dalaranian Empire. Though no means of bridging the two timelines has been made, the Empire has entered the "original" timeline on a number of occasions. It was created by Margrave Haifrall's Chronomancy at the time of his defection from the Kirin Tor.

Iron Horde Azeroth - Described in the Tales of the Infinite, this was an Azeroth that suffered the Iron Horde's invasion and lost the fight. This resulted in a conquest of Azeroth that led to the ultimate victory of the Iron Horde and downfall of virtually every power on Azeroth. This timeline briefly bridged itself into the "original" timeline with the events of Infinite Possibilities before the rift of the timeline was closed by the Magus Senate of Dalaran, after which the timeline supposedly collapsed.