ELI5: The many different types of atheism and what they mean, in a concise way

Only a few of what you listed are technically "types" of atheism in that they directly refer to the level of certainty in which a person claims to believe or disbelieve in a god/s. Those would be gnostic, strong, and de-facto atheists. They simply reference levels of certainty in which someone disbelieves - with strong and gnostic being pretty much the same as far as I'm aware (basically claiming 100% to know that god is a falsehood), and de-facto being "almost 100% certain." The main source of this spectrum, which also includes the opposite end of religious certainty, comes from Dawkins.

Most of the ideologies you listed are not technically the same as being atheist, but rather have logical conclusions that come from certain beliefs that inevitably lead to atheism. Personally I don't go as far as to consider them different "types" of atheism. In religion, the religion itself is not delineated by the reasonings of the people that have led them to believe, but rather, the tenets of the belief system. It is rather the manyfold flaws within religion itself that leads to multiple avenues for people to logically conclude that there is no higher power. I'll list a few examples but most can just be googled if you encounter one you are unfamiliar with - and the logical paths to a disassociation with religion can be traced for each one fairly easily.

Materialism would be the idea that all phenomena in the universe, including consciousness and other traditionally intangible things, come from matter. There would be absolutely no room for gods, as they are inherently non-material entities in their own belief systems.

Ignosticism is a linguistic requirement before a debate on god/s can take place. It calls to question the ambiguous and often undefined nature in which god/s are presented. Technically speaking this doesn't necessitate that a person be atheist to hold this as a belief - although it would be unusual - as belief in a god normally accompanies a personal definition of what that god is.

Nihilism by definition is the rejection of religious ideology and morality in light of the belief that there is no real meaning or real state to anything.

The TL;DR: As a general rule - if the phrase has atheist in it, it has to do with the level of certainty that a person has towards their own disbelief. If it does not, more often than not it is actually a philosophical or scientific set of principles that leads to the conclusion of atheism.

/r/atheism Thread