Discontinuity refers to conflicting accounts of various entities, places, events, or concepts in The Elder Scrolls.
In The Elder Scrolls II: Daggerfall, Arkay was originally mortal, and made immortal by Mara. From Morrowind onwards, this is not the case. But Runil says: "The god Arkay was once like us, bound to winding mortality. But he willingly gave up this existence that we might better understand the vagaries of life and death. It is through the ebb and flow of this cosmic tide that we find renewal and, in the end, peace. May the spirit of Lavinia and all those who have left this world and its suffering know the beloved serenity of Aetherius... and may we one day rejoin them in eternity."
It is mentioned throughout the series that Cyrodill was once covered in tropical jungles much like Valenwood or Elsweyr, but appears as temperate forest in The Elder Scrolls IV: Oblivion. This discontunity is explained however as the result of Tiber Septim achieving CHIM and erasing the jungles from history.
Lusty Argonian MaidEdit
The reason for this discrepancy is one of development choice. In Arena and Daggerfall, they were a small company, and they used a randomising program in order to create a large volume of characters in a relatively low cost and file size. By the time of The Elder Scrolls III: Morrowind, Bethesda Studios had been acquired by Zenimax, who provided them with the funding to produce the much more individualistic, hand-crafted approach to the genre that Bethesda are now known for creating.
There are multiple conflicting dates within the Timeline from different sources.