a generalization that describes recurring facts or events in nature

a principle of Gestalt psychology that identifies factors leading to particular forms of perceptual organization

the principle that if any change is imposed on a system that is in equilibrium then the system tends to adjust to a new equilibrium counteracting the change

(economics) the principle that when two kinds of money having the same denominational value are in circulation the intrinsically more valuable money will be hoarded and the money of lower intrinsic value will circulate more freely until the intrinsically more valuable money is driven out of circulation; bad money drives out good; credited to Sir Thomas Gresham

(physics) the principle that a measured quantity of mass is equivalent (according to relativity theory) to a measured quantity of energy

rule for calculating an expected delivery date; subtract three months from the first day of the last menstrual period and add seven days to that date