Absolutism has many different meanings. Absolute truth can mean a fact that is as close to objective Truth that we can get within a particular framework. Two plus two equals four.
But Absolute truth is also used by proponents of certain ideologies who claim that the tenets of their philosophy are absolute truths. This is certainly more subjective and fallible than a logical Absolute truth like “two plus two equals four.”
In moral, religious and philosophical contexts, an Absolute means something that is universally true. Again, this depends on who is making the claim and within which theoretical framework it is. Christians and Muslims may not agree on many truths, but there are some which they would both agree with. Each system of belief has its own absolute truths. So, other than logical propositions, like equations and a priori truths, most so-called Absolute truths are ideological and subjective.
If you see absolutist in a news article, chances are it refers to absolutist rule. This concept developed in 17th century France, but you still see examples of it today. Any place where there is strong or absolute control by a dictator or government body, it may be called Absolutist. Those who believe that their ideology is the best and that all others are so inferior that they need to be eradicated are fundamentalists. An Absolutist government/dictator often, but not always, operates under a fundamentalist philosophy.
But strictly speaking, in political contexts, an Absolutist authority has total control. Here, absolute means "total" or "complete."
In philosophical contexts, an Absolute is something so perfectly true that it transcends all categories and is true universally. It is true everywhere. Again, this depends on who is saying it and for what reasons. So, someone might call something an absolute truth to support their own philosophy or they might claim absolute rule because they believe their system of rule is the best.