There is no perfect answer to this question; the answer depends on particulars. (history is under no obligations to make language and terminology easy.)
An oversimplified, overly general model of power vacuums in a European monarchical systems, might include three terms that apply to the situation where there is no agent exercising executive power in a society:
Civil war - the most general case. Absence of executive power results in a struggle to name the agent of executive power.
Interregnum - if the civil war is confusing or protracted, historians may term it an interregnum - this is generally also associated with a decline in the institutions of government.
Regency - arguably, some cases of regency involve someone or something exercising custody of the executive power while waiting for a legitimate executive to arise.
"lack of mandate of heaven" This term is used in Chinese histories. This is not a literal term, but a metaphor for the absence of an effective emperor. The previous emperor is always castigated or accused of immorality, hence he fell from favor of heaven. No historian believes that per se, but it is just how the dynastic cycle of Chinese historiography is done. There are other Asian cultures this term refers only to the Chinese. (Hat tip to @J.Asia).
This answer is somewhat Eurocentric; I'm not competent to comment on Asian monarchies. If we extend this to non-autocratic rule, (tribal, nomadic, bigmen, theocratic, etc.) the situation becomes even more confusing.
Chinese dynastic cycles use the term "lack of mandate of heaven" (i.e. not literally of course, just how it is termed). As the previous emperor is always castigated or accused of immorality, hence he fell from favour of heaven. No historian believes that per se, but it is just how the dynastic cycle of Chinese historiography is done. There are other Asian cultures naturally, am just referring to the Chinese (the elephant)