Fideism is the doctrine that that biblically-informed Faith, particularly as related to Creation, is as legitimate a source of truth as Science. Fideism is therefore diametrically opposed to Materialism, the belief that only the material world is of consequence to truth, and Naturalism, the categorical rejection of that which cannot be explained by materialistic science. It is often associated with historical versions of Supernaturalism and is compatible with but not necessary to Creationism. 
The most vocal proponent of Fideism was Blaise Pascal, who argued that human reason (which would be natural theology within Christian epistemology) could not achieve complete certainty due to human error without the backing of divine revelation (revealed theology). In recent times, however, the doctrine has fallen out of use following the significant achievements of creation science in proving that the supernatural could be studied and proven through logic and science. Fideism has also been made unnecessary by Theistic realism, which argues that the claims of the Bible are in fact consistant with the laws of nature and that unaided human understanding of these laws, not the Bible, are at fault.