Occam's razor or Ockham's razor. noun: The maxim that the simplest of explanations is more likely to be correct.
[After William of Ockham (c. 1288-1348), a logician and theologian, who is credited with the idea.]
From Word-A-Day: Ockham's razor states that "entities should not be multiplied needlessly". It's also called the principle of parsimony. It's the idea that other things being equal, among two theories the simpler one is preferable. Why razor? Because Ockham's razor shaves away unnecessary assumptions. Ockham's razor has applications in fields as diverse as medicine, religion, crime, and literature. Medical students are told, for example, "When you hear hoofbeats, think horses, not zebras."