Douglas Harper's Etymology Dictionary
when two competing hypotheses explain the data equally well, choose the simpler. Or, as Sir William Hamilton puts it, "Neither more, nor more onerous, causes are to be assumed, than are necessary to account for the phenomena." Named for English philosopher William of Ockham or Occam (c.1285-c.1349), who expressed it with Entia non sunt multiplicanda praeter ncccssitatem.\n\nSo called after William of Occam (died about 1349): but, as a historical fact, Occam does not make much use of this principle, which belongs rather to the contemporary nominalist William Durand de St. Pourçain (died 1332).
[Century Dictionary]
Wikipedia
Occam's razor (also written as Ockham's razor, and lex parsimoniae in Latin, which means law of parsimony) is a problem-solving principle attributed to William of Ockham (c. 1287–1347), who was an English Franciscan friar, scholastic philosopher and theologian. The principle can be interpreted as stating Among competing hypotheses, the one with the fewest assumptions should be selected.
In science, Occam's razor is used as a heuristic technique (discovery tool) 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 or a scientific result; the preference for simplicity in the scientific method is based on the falsifiability criterion. For each accepted explanation of a phenomenon, there may be an extremely large, perhaps even incomprehensible, number of possible and more complex alternatives, because one can always burden failing explanations with ad hoc hypotheses to prevent them from being falsified; therefore, simpler theories are preferable to more complex ones because they are more testable.
Usage examples of "occam's razor".
Just apply Occam's Razor to your antimatter idea and you'll see what a lousy theory it is.
But Occam's Razor was a logical tool, not an inflexible condition of the universe, and it didn't hold good in all conditions.
It's time to shave with Occam's Razor, Boss, the simplest explanation is always the likeliest.
Because of Occam's Razor, a convenient and frequently used principle in science, but one that is not infallible.
The first one is the better assumption, according to Occam's razor.
It doesn't satisfy Occam's Razor, but in some moods it definitely satisfies me.
There's no point in trying to explain Occam's Razor to people who believe that UFOs are timeships from another century.
He even manages to reinterpret Occam's razor, the philosophical principle that explanations should be kept as simple as possible, to support his view.
As a scientific analyst Rachel Trehaine would naturally have considerable respect for Occam's razor.