Russell's teapot

Etymology
From a teapot described in an article written in 1952 by Bertrand Russell, “Is There a God?”.

Proper noun

 * 1)  A china teapot which hypothetically orbits the Sun between Earth and Mars, which is too small to be detected by telescopes but cannot be proven not to exist.

Usage notes
Originally used as an analogy to demonstrate that the burden of proof for unfalsifiable claims lies on the one making an assertion to show that it is true, not on the one doubting it to show that it is false.