A parsimonious theory is a theory that is simpler than other competing theories because it introduces the least new assumptions about the subject in question. This scientific principle is based on choosing the simplest scientific explanation that fits the evidence.
The word "parsimonious" comes from the Latin word "parsimoniae." It is seen most often in the Latin phrase "lex parsimoniae," which is more commonly known as Occam's razor. The Occam in Occam's razor comes from William of Ockham, who popularized the theory. The razor refers to the act of distinguishing between two hypotheses either by shaving away unnecessary assumptions or cutting apart two similar conclusions to provide a simpler answer.