The KSA is an absolute monarchy.
Remember your history....divine right of kings. A concept still taken seriously in some corners of the world. In Arabic culture, a king is a regent divinely appointed and ruling through the grace of God alone; used to be like that in European culture until maybe 200-300 years ago. The Saudi King is best described as combination of King and Pope (at least as far as the KSA is concerned; his religious writ doesn’t apply beyond their borders). And in Sunni, the real power is with the clerics, unlike Shi’a, where the power is with the Ayatollahs.
Not that much difference, “Ayatollah” is a clerical title, roughly comperable to “Archbishop”.