“Authoritarianism is a form of government characterized by strong central power and limited political freedoms. Political scientists have created many typologies describing variations of authoritarian forms of government. Authoritarian regimes may be either autocratic or oligarchic in nature, and may be based upon the rule of a party or the military.” Will Wikipedia do for you?
If you want my personal definition it’s “society based around a centralised government or other state-like system with limited or no oversight by the general population”
And hey, at least my side never tried to make peace with the fascists , and didn’timmediately start collaborating with them as soon as they took over