A Clockoverse is a reality timeline that has been created by two other timelines fusing and playing over one another. These "streamlined realities" are combined one at a time by "Th'st'la", an ancient being that is unknown to all but the Hethe, so it can feed off of the release energy from the fusing. The events of each reality play atop each other like they would individually, leading to the same events having two different outcomes at once, letting this world "break".
No beings can enter or leave these worlds except those aided by the Skethe, who do not follow the guidelines of existence put on these streamlined realities. Those that exit these are called "jumpers".