Occam's Razor (or Ockham's Razor) is the philosophical principle which states: entities should not be multiplied beyond necessity. In layman's terms this means "Out of several equally good explanations, pick the simplest one." In this definition, the word "simplest" means "the explanation that contains the fewest assumptions." For example, let's say a child contracts a nasty disease which leaves her in terrible pain. She is taken to the doctor's and is given medicine. Meanwhile, the parents pray to God for her safe recovery. Sure enough, a few days later she is perfectly healthy again and the parents, in their happiness, proclaim "God saved our child!" A better explanation for the child's recovery, however, would be that the medicine the doctors gave her did its job. When one compares the two explanations ("God did it" and "The medicine worked") one can see that the second requires fewer assumptions. God isn't required for the medicine to have worked in the second explanation, therefore it is the one that should be chosen.