A constant field in a class is similar to a global or function constant, except that it is scoped to the class and it can have various modifiers governing its visibility and usage.

It's a state function, so we're at constant temperature and pressure, and now we want to consider some chemical change or a phase transition or you name it.

Today, he has recovered enough to function without constant care, but seizures and other health problems have sent him to the er four times in recent months.