Can anyone give me a good definition as to how to tell the difference between a constant and a variable. For instance, the number of windows in a house is a constant.

A constant will not change, ever.

A variable is always subject to change.

If you're talking about 1 particular house at a given moment in time, yes, the number of windows is a constant. But a homeowner always has the option to add or remove windows, right?

If you're talking about the number of windows in a certain population of houses, then it's a variable.

Do you have some specific questions around this?