Wiktionary
n. (context physics English) A physical quantity that is generally believed to be both universal in nature and constant in time.
Wikipedia
A fundamental physical constant is a physical quantity that is generally believed to be both universal in nature and constant in time. It can be contrasted with a mathematical constant, which is a fixed numerical value, but does not directly involve any physical measurement.
There are many physical constants in science, some of the most widely recognized being the speed of light in vacuum c, the gravitational constant G, Planck's constant h, the electric constant ε, and the elementary charge e. Physical constants can take many dimensional forms: the speed of light signifies a maximum speed limit of the Universe and is expressed dimensionally as length divided by time; while the fine-structure constant α, which characterizes the strength of the electromagnetic interaction, is dimensionless.
Fundamental physical constant in the sense under discussion in this article should not be confused with other quantities called "constants" which are assumed to be constant in a given context without the implication that they are in any way fundamental, such as the " time constant" characteristic to a given system, or material constants, such as the Madelung constant, electrical resistivity, heat capacity, etc. listed for convenience.
Usage examples of "physical constant".
Beyond that, not every arbitrary choice of a law of Nature or a physical constant may be available, even to a maker of universes.
And once the way to do that became common knowledge, those hackers would move on, trying to make their universes develop the right kind of life, trying to find the one change in the Nth decimal place of some physical constant that would give us an Earth in which, say, Hitler had been accepted into art school after all, and had ended up his days as a street artist with cranky political opinions.