Interregnum (noun)

1. A period of time between two reigns or governments, especially a period of disorder or instability.
2. An interval between two regularly recurring events or processes.

Origin:

Latin interregnum, from inter- between + regnum kingdom.

Examples:

1. The interregnum was marked by civil war and political turmoil.
2. The interregnum between the fall of the Roman Empire and the rise of Charlemagne is known as the Dark Ages.
3. The interregnum between the old regime and the new democracy was a time of great uncertainty.
4. The interregnum between the end of one school year and the start of the next is a time for relaxation and rest.
5. The interregnum in the life of the nation was a time of great change and reform.