Here’s what Wikipedia has to say about it:
Occam's razor (or Ockham's razor) often expressed in Latin as the lex parsimoniae, translating to law of parsimony, law of economy or law of succinctness, is a principle that generally recommends, when faced with competing hypotheses that are equal in other respects, selecting the one that makes the fewest new assumptions
Overview
The principle was often inaccurately summarized as "the simplest explanation is most likely the correct one." This summary is misleading, however, since in practice the principle is actually focused on shifting the burden of proof in discussions. That is, the razor is a principle that suggests we should tend towards simpler theories (see justifications section below) 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.
Bertrand Russell offered what he called "a form of Occam's Razor" which was "Whenever possible, substitute constructions out of known entities for inferences to unknown entities."
Occam's razor is attributed to the 14th-century English logician, theologian and Franciscan friar Father William of Ockham (d'Okham) although the principle was familiar long before. The words attributed to Occam are "entities must not be multiplied beyond necessity" (entia non sunt multiplicanda praeter necessitatem), although these actual words are not to be found in his extant works. The saying is also phrased as pluralitas non est ponenda sine necessitate ("plurality should not be posited without necessity"). To quote Isaac Newton, "We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. Therefore, to the same natural effects we must, so far as possible, assign the same causes."
In science, Occam’s razor is used as a heuristic (general guiding rule) 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.
History
William of Ockham (c. 1285–1349) is remembered as an influential nominalist but his popular fame as a great logician rests chiefly on the maxim attributed to him and known as Ockham's razor. The term razor (the German "Ockhams Messer" translates to "Occam's knife") refers to distinguishing between two theories either by "shaving away" unnecessary assumptions or cutting apart two similar theories.
This maxim seems to represent the general tendency of Occam's philosophy, but it has not been found in any of his writings. His nearest pronouncement seems to be Numquam ponenda est pluralitas sine necessitate [Plurality must never be posited without necessity], which occurs in his theological work on the Sentences of Peter Lombard (Quaestiones et decisiones in quattuor libros Sententiarum Petri Lombardi (ed. Lugd., 1495), i, dist. 27, qu. 2, K).
In his Summa Totius Logicae, i. 12, Ockham cites the principle of economy, Frustra fit per plura quod potest fieri per pauciora [It is futile to do with more things that which can be done with fewer].
From Usenet Physics FAQ:
Stephen Hawking writes in A Brief History of Time:
"We could still imagine that there is a set of laws that determines events completely for some supernatural being, who could observe the present state of the universe without disturbing it. However, such models of the universe are not of much interest to us mortals. It seems better to employ the principle known as Occam's Razor and cut out all the features of the theory that cannot be observed."
"If you have two theories that both explain the observed facts, then you should use the simplest until more evidence comes along"
"The simplest explanation for some phenomenon is more likely to be accurate than more complicated explanations."
"If you have two equally likely solutions to a problem, choose the simplest."
"The explanation requiring the fewest assumptions is most likely to be correct."
In other words,"Keep things simple!"
