The phrase "brute fact" refers to a simple and undeniable truth or reality, without any need for further explanation or reasoning. It is a fact that is evident and doesn't require any justification. Full definition
Thus, in reality there would be only «accident and necessity,» nothing else, and one may only look upon these elements as brute facts. (firstthings.com)
Yet I must admit that my readiness to use objectivist language more freely than he does may have its roots (at least in part) in an eagerness, in questions of general epistemology, to endorse the views of those who emphasize the element of discovery in coming to know, and the authority of brute fact in the refutation of hypotheses. (religion-online.org)