There is no context so I will just explain what a constant is:
In an experiment following the scientific method, a constant is a variable that cannot be changed or is purposely not changed during the experiment.
An example would be:
If a researcher wanted to study the effects of temperature on the growth and development of garden snakes, the experimental variable for the experiment would be temperature. All other variables would need to remain consistent to avoid invalid data. The size of the cage, amount of light, food and many other variables would need to remain constant to ensure accurate results and a valid study. Those variables are constants. Some variables are not under a scientist's control, but are still considered to be constants. These constants are called universal constants and include gravity, the speed of light and electronic charge. Universal constants do affect experiments but will be constant through an experiment without being controlled by the scientist.
