The 10,000 Dawns is a collection of roughly 10,000 universes that are connected due to being different versions of the Prime Universe, which sits at their center. The 10,000 Dawns, often abbreviated to 10KD, are unusual and far more vast than the name implies in that, while they are a part of the multiverse, they are their own "bubble" multiverse, each being interconnected by the Bifrost Path and cared for by a species called the Firmament.
A list of Dawns can be found here.
The 10,000 Dawns was a portion of the multiverse which was constructed and controlled by the Firmament. (REF: Malflick the Wizard's Repost Emporeum, ) Within Pathway's story in the 10,000 Drafts, she believed that “10,000 worlds” had been created using the Creation Machine by the Infinite, (PROSE: Prototype) her timeline's equivalents of the Firmament. (PROSE: The Forgotten Heroines of 10,000 Dawns Big Takeover!) The Superiors of the Totality challenged the 10,000 Dawns' right to exist but were reluctantly convinced to let it be. (PROSE: Winter's View)