Term used to describe many religionists who insist that God (or any other spiritual entity) is hiding just beyond what's been discovered by scientists. That is, in the gaps of scientists' understanding.
For example, suggesting that soul has free will, and pointing to Quantum Mechanics as a basis (because we have not been able to prove that Quantum Mechanics is deterministic yet) is an example of resorting to the God of the Gaps.
See also Scientist's God of the Gaps.