Natural Theology, broadly defined, is that part of philosophy which explores that which man can know about God (his existence, divine nature, etc.) from nature via His divinely bestowed faculty of reason, and this, unaided by any divinely inspired written revelation from any religion, and this, without presupposing the truth of any one religion.

“NATURAL THEOLOGY AND PROTESTANT ORTHODOXY” by David Haines in God of our Fathers: Classical Theism for the Contemporary Church, Ed. Brad Little John, 57.