Freethought is a philosophical viewpoint that opinions should be formed on the basis of science, logic, and reason, and should not be influenced by authority, tradition, or dogma.

Atheism ("a" + "theism") means a rejection of belief in the existence of a god or gods. It can also refer to the belief that there are no deities. Most inclusively, atheism is simply the absence of belief that deities of any kind exist. Some atheists refer to themselves as "non-theists."

Secularism is the idea that people, governments, and other entities should have the right to be free from religious rule and teachings or to be neutral in regard to matters of belief.

Humanists believe all humans have the ability and responsibility to lead ethical lives that aspire to the greater good of humanity. They are committed to diversity, equality, an open and secular society, and to protecting the integrity and sustainability of our planet's resources.

Agnostics separate out belief from actual knowledge. They think it is impossible or not currently possible to prove the existence or non-existence of any deity, creative force, or other religious belief. Agnosticism may also refer to having a skeptical approach to such questions.

Deists believe that observation and reason suggest the existence of a higher power that created the universe and the scientific laws by which it operates, and then ceases to interfere.  Think of a watchmaker who creates and winds a watch, then retires. 

Naturalism is the viewpoint that the laws of nature, as opposed to supernatural laws, are all that operate in the universe. Steve Irwin, Rachel Carson, Charles Darwin, and Beatrix Potter were all naturalists.

Ietsism is is a loanword from Dutch, where "iets" (pronounced like the English word "eats") means "something". Ietism is an unspecified belief that there is "something" out there, but do not subscribe to a deity offered by any particular religion.