Interregnum

Definition: an interval between reigning monarchs; a disruption of continuity

The word literally means “between reigns.” If a ruler died, the interregnum was the period of time until a new ruler was crowned.

It can be used in general to refer to a gap in something otherwise continuous.

Why I Looked It Up

From Spam: A Shadow History of the Internet:

Though we some to have come a very long way from Peter Bos’s message of conscience to the terminal support by MIT, this history can also be read as a kind of interregnum, a transit from one period of overt control by systems administrators to another.