Definition
Parsimony is the value placed on economy in explanation: given a choice, prefer the model that explains the most while assuming the least. It is the broader principle that Occam's razor expresses as a practical rule.
Parsimony is not a worship of simplicity for its own sake. A parsimonious explanation must still fit the evidence. The aim is the best ratio of explanatory return to assumed complexity — not the simplest possible story, but the simplest story that actually works.
Why it matters
How it works
To apply parsimony, weigh each explanation by two measures at once: how much it accounts for, and how much machinery it needs to do so. Trim assumptions that earn nothing. Keep the ones that the evidence demands.
The discipline is iterative. You add complexity only when reality forces it, and you remove it whenever a simpler structure covers the same ground equally well.