Agnosticism is the position that is not possible to have knowledge of God. Often agnosticism is used catachrestically to broadly refer to other areas where one believes that knowledge is not possible, and therefore a clear conclusion is not possible.
The relationship between atheism and agnosticism is disputed. One view is that atheists are certain about God's nonexistence, while agnostics take the position that we cannot determine the answer. Another view is that the question of atheism and theism is separate from the question of agnosticism - and that agnosticism talks about whether or not knowledge of God is possible, while the question of atheism or theism is a question of belief. Therefore, under this second definition, one could be an "agnostic theist" - a person who believes that God exists, but states that knowledge of God is not possible. The certainty with which atheism is held is often demarcated with the terminology of strong and weak atheism. In other areas, the consequences of lack of knowledge differ based on both practical and philosophical presuppositions. Agnostics also differ on whether or not knowledge is forever unattainable, or simply currently not known. In the former case, there are often philosophical reasons that are given as to why knowledge can never be obtained.
The concept of agosticism is an old one, but the word itself is comparatively recent. It was coined in 1870 by T.H. Huxley, from the Greek α-, a- "not" and γνωστος, gnostos, "known". Huxley's circle of fellow agnostics include Herbert Spencer, William Kingdon Clifford, John Tyndall and Leslie Stephen.