William of Ockham (c. 1288 – c. 1348) was an English Franciscan friar and scholastic philosopher, who is believed to have been born in Ockham, a small village in Surrey. He is considered to be one of the major figures of medieval thought and was at the centre of the major intellectual and political controversies of the fourteenth century. Although he is commonly known for Occam's razor, the methodological principle that bears his name, William of Ockham also produced significant works on logic, physics, and theology. In the Church of England, his day of commemoration is 10 April.
The principle of Occam's razor is often summarized as "simpler explanations are, other things being equal, generally better than more complex ones." In practice the principle is usually focused on shifting the burden of proof in discussions. That is, the razor is a principle that suggests we should tend towards simpler theories until we can trade some simplicity for increased explanatory power. Contrary to the popular summary, the simplest available theory is sometimes a less accurate explanation. Philosophers also add that the exact meaning of "simplest" can be nuanced in the first place.
In science, Occam’s razor is used as a heuristic (general guiding rule or an observation) to guide scientists in the development of theoretical models rather than as an arbiter between published models. In the scientific method, Occam's razor is not considered an irrefutable principle of logic, and certainly not a scientific result.
Source: Wikipedia, "William of Ockham", available under the CC-BY-SA License.